Marine Fisheries Review 1994: Vol 56 Iss 3

33 Pages·1994·11.4 MB·English

yw. Marine Fisheries
REVIEW “s
National Oceanic and Atmospheric Administration * National Marine Fisheries Service
THE SOUTH AFRICAN (CAPE) FUR SEAL
Marine Fisheries
—
gym ae On the cover: The
South African (Cape) fur
S Nwaosn" seal, Arctocephalus pusillus
pusillus (photograph by P. Wickens).
oF
56(3), 1994
Articles
Trawling Operations and South African (Cape) Fur Seals,
Arctocephalus pusillus pusillus Patti A. Wickens and Peter F. Sims
King Mackerel, Scomberomorus cavalla,
Mark-recapture Studies Off Florida’s East Coast H. Charles Schaefer and William A. Fable, Jr.
Observations of the 1992 U.S. Pelagic Pair
Trawl Fishery in the Northwest Atlantic Patricia Gerrior, Amy S. Williams, and Darryl J. Christensen
U.S. DEPARTMENT OF The Marine Fisheries Review (ISSN 0090-1830) is of Management and Budget.
COMMERCE published quarterly by the Scientific Publications Of- The NMFS does not approve, recommend, or endorse
fice, National Marine Fisheries Service, NOAA, 7600 any proprietary product or proprietary material men-
Ronald H. Brown, Secretary Sand Point Way N.E., BIN C15700, Seattle, WA tioned in this publication. No reference shall be made to
98115. Annual subscriptions are sold by the Superinten- NMFS, or to this publication furnished by NMFS, in
NATIONAL OCEANIC AND dent of Documents, U.S. Government Printing Office, any advertising or sales promotion which would indi-
Washington, DC 20402: Annual subscription $8.00 cate or imply that NMFS approves, recommends, or en-
ATMOSPHERIC ADMINISTRATION domestic, $10.00 foreign. For new subscriptions write: dorses any proprietary product or proprietary material
New Orders, Superintendent of Documents, P.O. Box mentioned herein, or which has as its purpose an intent
D. James Baker, Under Secretary 371954, Pittsburgh, PA 15250-7954. to cause directly or indirectly the advertised product to
for Oceans and Atmosphere Publication of material from sources outside the be used or purchased because of this NMFS publica-
NMFS is not an endorsement and the NMFS is not tion. Second class postage is paid in Seattle, Wash., and
National Marine Fisheries Service responsible for the accuracy of facts, views, or opinions additional offices. POSTMASTER: Send address changes
of the sources. The Secretary of Cc has deter- for subscriptions for this journal to: Marine Fisheries
Rolland A. Schmitten, Assistant mined that the publication of this periodical is necessary Review, c/o Superintendent of Documents, U.S.
Administrator for Fisheries for the transaction of public business required by law of Government Printing Office, Washington, DC 20402.
this Department. Use of the funds for printing this peri- This issue, volume 56 number 3, was printed and dis-
Editor: W. L. Hobart odical has been approved by the Director of the Office tributed in February 1996.
Trawling Operations and South African (Cape)
Fur Seals, Arctocephalus pusillus pusillus
PATTI A. WICKENS and PETER F. SIMS
Introduction and Cawthorn, 1991). Less common are The South African (Cape) fur seal,
analyses of the losses to trawl fisheries Arctocephalus pusillus pusiilus, is the
The incidental take of marine mam- through interaction with marine mam- only breeding pinniped found in south-
mals during trawl operations has re- mals, although in South Africa this has ern Africa. This species, with a popula-
ceived attention in several countries, been documented and discussed (Shaugh- tion size of up to 2 million seals
including South Africa (Shaughnessy nessy, 1985; David, 1987; Wickens, (Anonymous, 1991), constitutes one of
and Payne, 1979), Alaska (Perez and 1989; Wickens et al., 1992). Such re- the largest fur seal populations in the
Loughlin, 1991), Canada (Pemberton et search has also revolved around the ex- world (Croxall and Gentry, 1987). Over
al., 1994), and New Zealand (Mattlin tent of consumption of fish discarded one-third of the total population ranges
by trawlers and the possibility that along the South African coastline
trawler offal supports the needs of part (Wickens et al., 1991), the area consid-
Patti A. Wickens is with the Marine Biology Re- of the population (David, 1987; Wick- ered in this study, while the remainder
search Institute, University of Cape Town,
Rondebosch 7700, South Africa. Peter F. Sims is ens et al., 1992), but not on cost of the is found off the Namibian coast. Off
with the Sea Fisheries Research Institute, Private losses from different fisheries. All stud- South Africa, seals are found at 10
Bag X2, Roggebaai 8012, South Africa. Views
or opinions expressed or implied are those of the ies of operational interactions between breeding colonies and 5 nonbreeding
authors and do not necessarily represent the po- seals and the trawl fishery in South Af- colonies (where pups are found only on
sition of the National Marine Fisheries Service, rica (Rand, 1959; Shaughnessy and an irregular basis). The largest and only
NOAA.
Payne, 1979; Shaughnessy, 1985; Ryan mainland colony is Kleinsee, where
and Moloney, 1988; Anonymous, 1987; two-thirds of the pups in South Africa
ABSTRACT—South African (Cape) fur Wickens, 1989; Wickens et al., 1992) are born (Wickens et al., 1991). Be-
seals, Arctocephalus pusillus pusillus, in- have focussed on the number of seals tween 1985 and prior to the cessation
teract with the South African trawl fisher- attending trawling operations and the of sealing in 1990, this was the only
ies—offshore demersal, inshore demersal,
numbers entrapped in the nets, and al- colony at which sealing occurred
and midwater fisheries. These interactions
take the following forms: Seals take or dam- most all have dealt with offshore dem- (Wickens et al., 1991).
age netted fish, on particular vessels they ersal trawling only. Wickens et al. In South Africa, the trawl fishery is
become caught in the propeller, seals drown (1992) reviewed research on all seal- the second largest contributor, after the
in the nets, live seals come aboard and may fisheries operational interactions in pelagic purse-seine fishery (28%, an
be killed. Except in specific cases of seals
South Africa, and this was followed by average of 172,000 metric tons (t) an-
damaging particular trawler propellers, in-
teractions result in little cost to the offshore an evaluation of these interactions in nually between 1988 and 1992 inclu-
and midwater trawl fisheries. For the in- South Africa (Wickens, 1993, 1994). sive), to the South African fishing in-
shore fishery, seals damage fish in the net Based on that study, this paper evalu- dustry in terms of the cleaned (mainly
at an estimated cost in excess of R69,728 ates the operational interactions be- headed and gutted) mass of fish landed.
(US$18,827) per year, but this is negligible
(0.3%) in terms of the value of the fishery. tween seals and each of the three trawl However, it is by far the largest (51%,
Seal mortality is mainly caused by drown- fisheries (offshore demersal, inshore an average of R260 million or US$74
ing in trawl nets and ranges from 2,524 to demersal, and midwater) separately, in million) in terms of financial value to
3,636 seals of both sexes per year. Between terms of financial cost to the industry the industry (data from Sea Fisheries,
312 and 567 seals are deliberately killed
(from catch losses, gear damage, and Cape Town). Within the fishing indus-
annually, but this most likely takes place
only when caught and they enter the area operational disturbance) and mortality try this sector involves the largest num-
below deck, where they are difficult to re- or injury to the seals (through inciden- ber of personnel (almost 9,000), one-
move, and pose a potential threat to crew tal and deliberate killing) in South Af- third of whom are fishermen operating
safety. Overall, seal mortality during trawl- rican waters. This is done by evaluat- on trawlers.
ing operations is negligible (0.4—0.6%) in
ing new data and by making compari- The trawl sector is divided into off-
terms of the feeding population of seals in
South Africa. sons with published studies. shore and inshore demersal trawling
56(3), 1994
and, since 1989, midwater trawling Midwater trawling targets mainly Observations of offshore and inshore
(Fig. 1). Prior to 1991 there was also an Cape horse mackerel, Trachurus tra- demersal trawling were made from both
experimental demersal longline fishery. churus capensis (Crawford, 1989). commercial and research trawlers, but
During that longlining, an estimated There is no total allowable catch, but to the data from the two types of vessel
5.3% of the catch was lost to seals place some limitation on the exploita- are not directly comparable. The re-
(Wickens et al., 1992), and this was tion of this species, a maximum annual search vessel was a stern trawler which
considered a significant quantity. Off- catch is recommended. In 1992 there trawled for a period of 30 minutes, a
shore demersal trawling provides by far were seven vessels, all stern trawlers, shorter trawl time than done by com-
the greatest landed mass and landed licensed for midwater trawling, but mercial vessels. Research trawls were
value of fish. The masses of fish landed most were not exclusively involved in made using a net with a 27 mm (10.6-
by the inshore demersal and midwater midwater trawling. Midwater trawling inch) mesh liner as opposed to mini-
trawl sectors are similar, but the value is done mainly at night. mum commercial net mesh restrictions
of the inshore trawled fish is greater. of 110 mm (43.3 inches) and 75 mm
Data Collection
Offshore demersal trawling targets (29.5 inches) to the west and east of
the two species of Cape hake, Merluccius Quantitative information through in- Cape Agulhas, respectively. The two
capensis and M. paradoxus, for which dependent surveys was required in sets of data were analyzed separately,
there is a single total allowable catch; which observers record counts of seals with the research data being used for
kingklip, Genypterus capensis, is caught and incidences of entrapment during comparison only.
as a by-catch (Payne, 1989). In 1992 there trawling operations aboard commercial During 1992 observers made nine
were 58 active offshore trawlers which vessels. Observers were briefed before demersal offshore trawling trips on
generally fish only by day. Most are stern leaving, the completed data sheets were commercial vessels, all but one of which
trawlers and a few are side trawlers. examined on their return, and any un- were on stern trawlers (Table 1). The
Inshore demersal trawling targets usual occurrences were cross-checked. observation period totaled some 64 days
hake and the Agulhas sole, Austro- Independent observations were possible at sea, during which about 600 t of
glossus pectoralis, for which there are on offshore trawlers, but there were lo- cleaned (mainly headed and gutted) fish
species-specific total allowable catches gistical difficulties in carrying out in- were caught. Observations were made
(Payne and Badenhorst, 1989). King- dependent observations at sea on in- during 222 hauls of the net. A further
klip is a by-catch, as in the offshore shore demersal and midwater trawlers. 75 days of observation took place on
trawl fishery. This form of trawling is
done with side trawlers, both day and
night. In 1992 there were 37 trawlers Table 1.—Details of commercial and research trips undertaken to observe seal interactions during trawling op-
actively used for inshore trawling. erations during 1992-93. Observations on the offshore and inshore trawlers were done by independent observ-
ers and those on the midwater trawler by the skipper.
Trip and Duration Observed
vessel Company Month (days) hauls
Long-line Offshore demersal
B@ Midwater trawl Commercial Jan.-July D> 222
0 inshore demersal trawl . Anemone 1&J' Jan. 26
H(0 Offshore ademersal trawl t . Harvest Galaxy Sea Harvest Feb. 30
. Erica 1&J Feb. “a 36
. Aloe 1&J Apr. 15
. Harvest Belinda Sea Harvest Apr. 21
. Begonia 1&J May
. Aloe 1&J June
. Aloe 1&J July NONOSHODOH
. Begonia 1&J July
Research Feb.-April
L(t)1a ,n0d0i0n gs 1. Africana Feb.
2. Africana April
+ 3. Africana Feb.
Total (12 trips)
| [ Inshore demersal
Commercial Jan.-July
1. Atlantic Privateer Mariette Fishing Jan.
2. F.V. Immanuel Mariette Fishing March
3. Atlantic Privateer Mariette Fishing May
4. Dunevegan Mariette Fishing Jan.
5. Barcelona P. Cronje Feb.
6. Mary Ann P. Cronje July
R(Vmaainlldulieso )n Research April-Sept.
4+ 1. Africana April
1988 1989 1990 1991 1992 2. Africana Sept.
Total (8 trips)
Figure 1.—Contribution of the sectors
within the trawl and demersal longline Midwater
fisheries in South Africa in terms of land- Com1.m eRrocxiaanla Bank JJuunnee--JJuullyy
ings and landed value over a 5-year pe-
riod (1988-92). ‘Irvin & Johnson
Marine Fisheries Review
the research vessel F:R.S. Africana in trapment and deliberate killing during “west” coast, defined as the region west
1992 and 1993, during which 131 off- 16 hauls in 1993 (Table 1). A discus- of Cape Agulhas, and the “south” coast,
shore demersal hauls were observed. sion and quantification of the interac- the region east of Cape Agulhas (Fig.
Six inshore demersal trawling trips tions are also provided, based on the 2). Most offshore trawling takes place
were undertaken in 1992 and 1994 data collection from the offshore dem- and most seal pups are born on the west
(Table 1). During the 27 days spent at ersal trawl observations. coast, and likewise most observation
sea, a catch of approximately 44 t of For all of the trawl fisheries, catches effort is concentrated in this region, with
cleaned fish were caught on 65 hauls, are expressed in terms of landed mass, less on the south coast. By contrast al-
all of which were observed. Conditions and economic calculations are made most all fishing effort by inshore trawl-
aboard inshore trawlers did not readily using landed values from 1992, the lat- ers is concentrated on the south coast,
allow for accommodation of additional est available data from Sea Fisheries, and all of the observer effort was done
personnel as observers. Hence, the num- South Africa. The South African cur- in this area, mostly within 50 miles of
ber of observed commercial hauls was rency of Rands is converted to U.S. dol- Mossel Bay. Midwater trawling also
limited. During 50 days at sea on two lars using an exchange rate of takes place mostly on the south coast,
research cruises on F:R.S. Africana dur- US$0.27:R1 as of July 1994. For later with a small quantity being done on the
ing 1992, records of seal activity were calculations, the total number of trawls west coast. In this region there are only
made during 72 inshore demersal hauls. during 1992 is used, and consisted of two breeding colonies of seals but trawl-
As aresult of the difficulties involved 42,374 offshore demersal trawls, 21,575 ing activity is close inshore.
in obtaining observations from commer- inshore demersal trawls, and 1,100 Offshore and inshore demersal trawl-
cial inshore trawlers and the fact that midwater trawls. ing is carried out consistently through-
damaged fish are not sorted at sea, a For discussion purposes, the South out the-year, and observations from
monitoring program was established to African coastline is divided into the commercial trawlers occurred during
record seal-damaged fish in the catches
at landing sites. This took place at the
Irvin and Johnson (I & J) and Sea Har-
vest! factories in Mossel Bay, the ma-
jor landing site for inshore trawlers.
Estimates of damaged fish and total
Kleinsee
landings were recorded by the same two
(65% of pups)
factory production supervisors at each South Africa
factory from May 1992 to April 1994.
These persons are not affiliated with the
vessels from which the fish are landed
and are therefore considered to be in-
dependent recorders. The mass of seal-
damaged sole and seal-bitten kingklip West coast islands
(33% of pups)
was recorded from a total of 991 land- Port
Cape Elizabeth
ings, during which time over 1,068 t of Town Cape
sole and over 133 t of kingklip were eo Agulhas
landed. South coast islands
(2% of pups)
On the smaller midwater trawlers it
was not possible to obtain a berth for Inshore
demersal Midwater ,
an observer, and the larger vessels only r Offshore
Oo demersal
make a few trips during which midwater 0+ + @ ra) 22
trawling may take place. For this rea-
+ QDo
son no independent observation data of
Offshore
seal interactions with the midwater demersal
trawl fishery were obtained. However, Pofe rctcroeamnwmltesa rgcei al Inshore Midwater -——Np+S o- Pofe rotcrbeasnweitrsav geed
one of the larger trawling companies demersal |
7 o
chose one of their skippers as an appro- West of Cape Aguihas East of Cape Aguihas
"west coast” “south coast"
priate and reliable person for collect-
T T
ing data. Observations were made by 16 18 22 4
this skipper as some indication of en-
Figure 2.—Distribution of commercial (1992) and observed (1992-94) trawls for the off-
shore and inshore demersal and midwater trawl fisheries. The location of the breeding (dot)
'Mention of trade names or commercial firms and non-breeding colonies (circle) of the South African (Cape) fur seal in South Africa are
does not imply endorsement by the National shown with the percentage of all pups born in South Africa for Kleinsee and the islands to the
Marine Fisheries Service, NOAA. west and east of Cape Agulhas.
56(3), 1994
the first half of the year when berths and number of seals counted when the the observers were likely to move be-
observers were available. Midwater codend of the net surfaces is taken as tween these trawlers. The size of seals
trawling also occurs through the year, the average number feeding. However, is difficult to estimate but only medium
but concentrated effort depends on the these counts of the actual number that (40-100 kg; 88-220 pounds) and large
availability of fish and the allocated may be pulling fish from the net are a (2100 kg; 2220 pounds) seals were re-
quotas. Observations of midwater trawl- minimum, because seals will also be ported. This was expected because
ing were made by the selected vessel at feeding below the surface and will not young, small seals are less likely to feed
midyear. be counted. Seals counted are likely to far from the coast.
move between different trawlers work- The following two points regarding
Seal Attendance ing in an area, and therefore this num- offshore demersal trawling are noted,
Seal counts were made by observers ber cannot be multiplied up by the num- and both are postulated, based on our
at commercial offshore and inshore de- ber of trawlers to establish total num- knowledge of seal distribution and
mersal hauls; they include seals around bers of seals feeding in an area. behavior:
the trawler, i.e., not only at the stern or First, more seals attend offshore
Offshore Demersal Trawling
side where the net was hauled. No trawling operations on the west coast
counts of seals were made during Seals were seen on the majority than on the south coast. On the south
midwater trawling. Fish processing and (>84%) of observed offshore demersal coast, offshore trawlers are restricted
discard release take place throughout hauls and more frequently on the west from trawling in water <110 m (<360
the trawling process, so seal attendance coast. On both the west and south feet), and this includes the Agulhas
includes seals that are feeding on such coasts, it was most common for observ- Bank which extends 180 n. mi. offshore
discards. For offshore trawlers it is as- ers to see <5 seals/haul, but on the west in places. On the west coast trawling
sumed that the number of seals attend- coast many more were also seen on oc- takes place closer inshore and it is there-
ing side trawls is the same as at stern casion (Fig. 3). If the maximum num- fore more accessible to the seals. The
trawls, so these data are combined. ber seen during a haul is considered, observations show a mean of 18 seals
The numbers of seals counted dur- most observations were of 11—20 seals (with a maximum of 260) on the west
ing different stages of the trawl are at a trawl on the west coast and fewer coast and a mean of 3 (with a maximum
shown in Table 2. Seals are most likely on the south coast. On 40% of the ob- of 10) on the south coast; this differ-
to take fish from the time the net nears served commercial trawls, other trawl- ence is significant (Kruskal-Wallis test
the surface until it is hauled aboard. The ers were visible and the seals seen by statistic = 35.7, P<0.001). Shaughnessy
Table 2.—Observed number of seals around offshore and inshore demersal trawl- Offshore demersal
ers during different stages of a trawl. No counts were made from midwater trawlers.
The minimum count in each case was zero.
West coast
Number of seals observed
Stage of trawling operation Mean + 1 S.E. Max.
Offshore demersal
West coast
Commercial (n = 185)
Trawling (Shooting to net at depth) 4+0.74
Start hauling net 15+2.28 South coast
Otterboards on vessel 1642.13
Codend surfaces 18 + 2.06
Net aboard 18+ 1.84
Mean: Hauling to net aboard 16+ 1.99 (J Mean number
Research (n = 102) SS Maximum number
Codend surfaces 2+0.40
South coast
Commercial (n = 37)
Trawling (Shooting to net at depth) Inshore demersal
Start hauling net
Otterboards on vessel
Codend surfaces ooPfbe srecrevnattaigoen s
Net aboard
Mean: Hauling to aboard
Research (n = 30)
Codend surfaces
Inshore demersal
Commercial (n = 65)
Trawling (Shooting to net at depth)
Start hauling net 1-5 6-10 11-20 21-30 31-50 51-100 >100
Otterboards on vessel
Codend surfaces Number of seals observed during a haul
Net aboard
Mean: Hauling to aboard
Research (n = 72) Figure 3.—Numbers of South African fur seals observed at off-
Codend surfaces shore and inshore demersal trawling operations in South Africa.
Marine Fisheries Review
and Payne (1979) recorded differences medium (40-100 kg; 88-220 pounds) an average trawl time of 2.2 hours. The
of a mean of 6 seals on the west coast and large (2100 kg; = 220 pounds) seals time of 2.1 hours observed from the net
and 4 on the south coast during com- were reported, although a few small depth to the start of hauling, as recorded
mercial trawling. Data from research (<40 kg; 88 pounds) seals were also from observations (Table 3), therefore
trawls indicate double the number of seen. It is probable that the presence of indicates that the observed trawls were
seals on the west coast (2 with a maxi- small seals results from the proximity probably typical of offshore trawling.
mum of 30) compared to the south coast of trawlers to the coast, where younger While seals may eat large quantities
(1 with a maximum of 6). Other counts seals are found. of fish near the net (one seal was ob-
of seals from research trawls that have As with offshore trawling, signifi- served eating 24 free-floating fish),
been documented are: on the west coast, cantly more seals accompany the in- fish damage attributable to seals in off-
8 (Ryan and Moloney, 1988) and 10 shore trawlers from the time the net shore-trawled catches is considered
(Shaughnessy and Payne, 1979); and, starts being hauled than when the ves- negligible.
on the south coast, 3 seals (Shaughnessy sel is trawling (Wilcoxon test statistic
Inshore Demersal Trawling
and Payne, 1979). Fewer seals are seen = 5.29, P<0.001). The mean number
at research trawls than commercial seen before the net is hauled is 2 seals During inshore trawling, the average
trawls. This is likely to be related to dif- (with a maximum recorded of 22), time period that seals have to feed on
ferences in trawl time, mesh size, and whereas the mean number seen when fish in the net when the codend lies on
the fact that research trawls are made the codend surfaces is 9 (with a maximum the sea surface is 8 minutes, although a
in random areas, often out of the com- of 27 seals). By comparison, on research maximum of 25 minutes was also re-
mercial trawling grounds, with no re- trawls the mean was 2 seals with a maxi- corded. This commercial trawling effort
gard for fish density, whereas commer- mum of 10 when the codend surfaced. is also measured in hours (from the net
cial trawls seek to operate in areas with reaching depth to start of hauling) and
Feeding
fish concentrations. a total of 77,425 hours was spent in-
Second, many seals arrive only when Seals were seen taking fish sticking shore trawling in 1992 during 21,575
the hauling starts. Indeed, seals may be through the net and scavenging mori- hauls. This produced an average trawl
attracted to the trawlers by the sound of bund fish that floated free of the net time of 3.6 hours. The time of 3.5 hours
the winch starting to haul the net. Cur- (Fig. 4). Damaged fish are separated on from the net at depth to the start of haul-
rent data confirm this, in that there is a board, but it is not possible to determine ing as recorded from observations there-
significantly greater number of seals how much of the damage was attribut- fore indicates that the observed trawls
present from the time the net starts be- able solely to seals. Damage to fish, and were probably typical of inshore trawls.
ing hauled until it is aboard compared in particular to offshore trawled fish, Records of damaged fish made at the
to when the vessel is trawling (Wil- also results from constriction of the net factories show that a greater proportion
coxon test statistic using ranks = 0.14 and the pressure of the fish mass, par- of kingklip is damaged than sole (Fig.
for the west coast and 4.92 for the south ticularly during hauling. 5). This is most likely to be at least par-
coast, P<0.001). On the west coast, The duration of each stage of a trawl tially attributable to the fact that sole
there was a fourfold difference between was recorded during all commercial can be pulled through the net easily and
these stages of the operation (from 4 to trawls (Table 3). The time from the net in this way can be removed whole (and
16 seals), and on the south coast, num- surfacing to its being hauled aboard is therefore are not recorded in the catch),
bers changed from no seals to an aver- the minimum period during which seals whereas seals can only bite those parts
age of 2 seals. may feed from the net. Seals may feed of kingklip that protrude through the
from the net while it is being brought net.
Inshore Demersal Trawling
to the surface, and they also feed on Spoilage of sole and kingklip by seals
Seals were seen on the majority floating fish or discarded fish once the is not significantly correlated to monthly
(95%) of inshore demersal hauls ob- net has been hauled. sole and kingklip landings, respectively
served, and in two-thirds of the ob- (r[sole] = 0.359, r{kingklip] = 0.445,
Offshore Demersal Trawling
served hauls the mean number seen was n=12, P > 0.05) so the extent of spoil-
no more than five (Fig. 3). In terms of In offshore side trawling, the net, or age is likely to be related to both the
the maximurn number of seals recorded part of it, lies on the surface longer at time that the codend stays on the sur-
during any haul, on over one-third of the end of a haul than in offshore stern face and the number of seals attending
the hauls there were 1-5 seals, and on trawling. In offshore trawling this pe- each haul. In both cases the fish are
just more than one-fifth of the hauls riod averages 18 minutes for side trawls trimmed to remove the damaged portion,
there were 21-30 seals per haul. As and 5 minutes for stern trawls. Com- and this results in some financial loss.
during offshore trawling, seals are likely mercial trawling effort is measured in Damage to sole averaged 0.7%, vary-
to move between trawlers working in hours (from the net reaching depth to ing between 0.3 and 1.3% of the land-
an area, and an average of six trawlers start of hauling), and in 1992 a total of ings per month with the lowest losses
were visible at every haul. Estimates of 92,602 hours was spent offshore trawl- recorded during June, but the reason for
the size of seals indicated that mostly ing during 42,374 hauls. This results in the fluctuations are not clear. Sole are
56(3), 1994
Figure 4.— South African fur seals feeding at an offshore demersal trawl net. Many seals may feed from
the net, particularly on the west coast of South Africa (top; photo by P. Bibb), however fewer are fre-
quently seen (bottom; photo by J. Enticott).
Marine Fisheries Review
Table 3.—Observed duration in minutes of different stages of offshore and inshore
demersal trawis. The difference in the time taken between the codend reaching the
surface and the net being aboard is given separately for stern and side offshore
trawlers.
Duration (minutes)
Stage of trawling operation Mean + 1 S.E. Min. Max.
Offshore demersal (n = 222)
Shooting net —> net at depth 2140.47
Net at depth —> start hauling net 123 + 2.62
Start hauling net —> doors on vessel 14+ 0.47
Otterboards on vessel —> codend surfaces §+0.20
Cod end on surface —> net aboard (stern, n = 192) 5+0.22
f(Latata) cn tdoirny gs
Cod end on surface —> net aboard (side, n = 30) 18+ 1.28 istlshae anatd li-ndgas maged
Total : Start hauling to net aboard 25+ 0.74
Total : Duration of trawl 171+2.89 ((skoaP(fiofne[ inl]drg)e) ck leinpt age
Inshore demersal (n = 65)
Shooting net —> net at depth 9+0.39
Net at depth —> start hauling net 210 + 7.62
Start hauling net —> doors on vessel 10 + 0.39 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Otterboards on vessel —> codend surfaces 6+ 0.26
Cod end on surface —> net aboard 8+ 0.65 Figure 5.—Monthly inshore demersal trawl landings and the quan-
Total : Start hauling to net aboard 23 + 0.90 tities of sole and kingklip that are seal-damaged, as recorded from
Total : Duration of trawl 242 *7.36 two factories in Mossel Bay during this study. The numbers indi-
cate the number of landings examined.
most commonly marketed with the head trimming. On average, 11.7% of the tionally less of the catch is available to
on, so seal-damaged fish which may be catch was damaged by seals which is a the seals. Spoilage of fish is therefore
missing a portion of the body and head loss of 3.9% of the mass prior to land- considered to be negligible.
(Fig. 6a) are sold for a lower price per ing. Although the 1992 landings were
Equipment Damage
unit mass. The reduction in price of a 200 t, the potential landing, if no seal
damaged fish depends on the initial size damage had occurred, could have been Net damage by seals is not generally
of the fish, because prices per fish are 208.1 t, providing an estimate of dam- considered to be a problem during any
size-dependent. On average, sole were aged kingklip at 8.1 t. At the 1992 form of trawling. Observers did note,
considered to be reduced in price by landed price of R5.76(US$1.56)/kg, as a matter of course, the damage to
50%, although the vessels sometimes some R46,656 (US$12,597) would be fishing gear resulting from various
kept the seal-damaged sole to sell else- lost because of seals. causes, but only on an offshore trawler
where at a higher price. At least 5.6 t Overall the loss through seal depre- was minor net damage caused by a seal
(0.7%) from the 1992 landings (797 t) dation of sole and kingklip is calculated when it attempted to free itself from the
were estimated to be seal-damaged, al- as R69,728 (US$18,827). This does not net (0.5% of offshore trawls). Both off-
though this is an underestimate because include fish that are pulled through the shore and inshore demersal nets were
whole sole may be pulled from the net net mesh by seals and lost (particularly occasionally torn during observations,
by seals and not recorded at the factory in the case of sole which can be pulled either from dragging on the bottom or
amongst the damaged fish. The landed from the net whole), damage to other from rocks that were brought up. The
price of sole in 1992 was R8.24 species, or damaged fish that are not size of the tears varied, as did the time
(US$2.22)/kg. If this damaged mass landed. It can therefore be regarded as taken to repair them.
were sold at half price then the loss a minimum. The propellers of some offshore de-
would be R23,072 (US$6,229). mersal trawlers are mounted in Kort
Midwater Trawling
Kingklip damage varied between 4.4 nozzles which increases suction. Seals
and 15.3% of the landings and was no- Midwater trawls may last from about feeding beside such vessels can be
ticeably lower in February and Novem- 10 minutes to a few hours, depending sucked into the nozzle and damage the
ber/December, but the reasons for this on depth and visibility of the fish; they propeller by bending or breaking off a
are not known. Kingklip is marketed in averaged 2.6 hours during the observa- part, and this may be costly. A trawler
various forms so seal-damaged fish tions in this study. The smaller mesh of with a damaged propeller increases fuel
(Fig. 6b) is only regarded as a loss of the midwater trawl net means that less consumption of the vessel, requires in-
mass, not a loss in the price per unit of the entrapped fish protrude, and they spection by a diver, and may require
mass. For kingklip it is assumed that a are therefore not easily accessible to repair or replacement. At least one-third
third of the mass of each damaged fish seals. The larger catches made by of the vessels owned by the two major
is lost as a result of the seal bite and midwater trawlers mean that propor- trawling companies are fitted with Kort
56(3), 1994
Figure 6.—Seal-damaged sole (a) and kingklip (b) from the inshore demersal fishery. Photo a by P. Sims and Photo b by L. Taylor.
nozzles, but few complaints of seals have finely mincing the discarded fish so that which live seals were brought aboard.
been made by skippers. We suggest that it is less attractive for seals. In this way In eight of these, one seal was involved,
problems may be related to the specific it is hoped that seals will not feed near and in the remaining three there were
design of the vessel or to the position of the offal outlet and therefore will be less two seals. These incidents involved a
the offal outlet at which seals may feed. likely to be sucked into the nozzle. From total of 14 seals, averaging 7.6 seals per
Two I & J trawlers, in particular, have the trials carried out to date, the experi- 100 hauls. In two of the incidents a seal
reported such problems, and in 1991 ment has proven successful. managed to get below deck (1.1% of
both had the factory deck layout rede- hauls). In one case, fish boxes were
Live Seals Aboard
signed to move the outlet for discarded placed strategically to provide the seal
fish away from the propeller. In each Fishing operations may be disrupted with an escape route and it climbed out
case, the cost was about one million if live seals are brought aboard in the and left the vessel after about 90 min-
Rand (about US$250,000). However, net. Generally, returning live seals to the utes (Fig. 7). In the other case, the seal
the problem was not resolved and ob- sea is not a problem and, from observa- became trapped in the factory area, and
servers present during three trips on tions, in most instances the seals left the it was clubbed to death after removal
these vessels heard a thud and the engine vessel of their own accord or were attempts failed.
straining as a seal passed through or be- chased out by the crew. Most seals On the 37 observed south coast hauls
came stuck in the nozzle. On some occa- brought aboard do not go below deck, there was one incident (2.7% of hauls
sions there was blood in the water and but when this happens it can be a prob- average) of a single seal coming up in
injured seals surfaced. On one trip, the lem. Nevertheless, injuries resulting from the net. The time taken for the seals on
auxiliary power had to be brought in to seals aboard trawlers are not common. deck to leave the vessel generally var-
complete the trawl and the main engine ied from almost immediately to 45 min-
Offshore Demersal Trawling
was then reversed to release a dead seal. utes. An exceptional case was of a seal
In late 1992, one of the I & J vessels During the 185 offshore demersal which was thought to be injured taking
which had problems with seals was fit- trawls observed on the west coast, there over 5 hours to leave, having been
ted with a “crusher” to experiment with were 11 incidents (5.9% of hauls) in brought aboard during the last haul of the
Marine Fisheries Review