The impacts of bottomfishing on Raita and West St. Rogatien Banks in the Northwestern Hawaiian Islands

2006·5.4 MB·English

by  Christopher Kelley

THE IMPACTS OFBOTTOMFISHING ON RAITAAND WEST ST. ROGATIEN
BANKS IN THE NORTHWESTERN HAWAIIAN ISLANDS
BY
CHRISTOPHERKELLEY' AND WALTER IKEHARA-
ABSTRACT
The authors assessedthe impacts ofbottomfishing in the Raita and West St.
Rogatien Bank Reserve PreservationAreas (RPAs) in the Northwestern Hawaiian
Islands Coral ReefEcosystem Reserve (NWHICRER). The executive ordercreating
NWHICRER stipulates thatbottomfishing will be allowed in these RPAs only ifit is
determined notto be having an adverse impact on theirresources. In orderto address that
provision, known fishing sites onbothbanks were surveyed in 2001 using a submersible
and aremotely operated vehicle (ROV). One site from each bank subsequently was
selectedwhere three submersible dives were conducted in both 2002 and 2003. During
the dives, a standardizedprotocol was usedto obtain data on the abundance and size
ofbottomfish targetedby fishermen, amount offishing debris present at the sites, and
thet3T5es andabundance ofbenthic invertebrates andotherfish species thatcouldbe
impactedby fishing activities. In 2002, comparative data also were obtained from dives
in one otherRPA( Brooks Bank), two heavily fished sites in the Main Hawaiian Islands
(MHI), andtwo sites within the Kahoolawe Island Reserve where bottomfishing has
beenprohibited for over 8 years. The impacts resulting from bycatch, lost fishing gear,
anddiscardedtrash are relatively low. Thepopulations ofone bottomfish species, onaga
(Etelis coruscans), couldbe decreasing on Raita Bank, although previous estimates of
maximum sustainable yield indicate the numberbeing taken is sustainable.
INTRODUCTION
TheNWHICRERwas created in 2001 by President Clinton's Executive Order
(EO) 13178. Within the reserve, nine islets/atolls and six banks were designated as RPAs,
eachhaving its own additional layer ofregulations regardingusage and access. Two of
these RPAs, RaitaBank andthe firstbankwest ofSt. Rogatien Bank (WSR Bank) have
the specific condition that after 5 years, bottomfishing will be allowed to continue only if
itis determinedthatithas no adverse impactontheresources ofthese banks. Commercial
bottomfishingtargets seven species ofsnappers (familyLutjanidae), one grouper(family
Serranidae), and onejack (family Carangidae).All but one ofthese species are typically
HawaiiUnderseaResearchLaboratory, 1000PopeRoad,MSB303,Honolulu,HI96822USA,
E-mail: [email protected]
-DepartmentofLandandNaturalResources, StateofHawaii, 1151 Punchbowl Street, Room330,
Honolulu,Hawaii96813 USA
306
m
caughtwith hook and Hne at depths of100 ormore. The exception, uku {Aprion
virescens), is caughtby surface trolHng overthe tops ofthe banks well above thatdepth.
In 2001, a 3-yearstudy was initiated to address thebottomfishing provisions in
the EO for Raita andWSR Banks. Acomprehensive report on the findings from this
study, along with recommendations regarding the continuation ofbottomfishing in these
two RPAs, was submitted to federal and state management agencies inAugust 2004. In
thispaper, we summarize the content ofthatreport forawideraudience.
MATERIALSAND METHODS
Potential bottomfishing impacts were classified into three categories: additions,
removals, and alterations. "Addition" impacts included man-made materials found on
the sites ofwhich there were two types: a) lost fishing gearsuch as fishing lines, hooks,
weights, and anchors; and b) trash such as beverage cans, bottles, plastics, metal objects,
and cloththatmay have been discardedbyfishers ormayhave come from othersources.
Removal impacts included reducednumbers oftargetedbottomfish species as well as
nontargeted or"bycatch"" species that were caught, killed, and eitherkept ordiscarded.
Alteration impacts were considered to be eitherdirect or indirect. The former included
damage causedbyfishing gearto the substrate orbenthic invertebrates, particularly
attached cnidarians and sponges. Indirect alterations were consideredto be changes in the
community structure as aresult ofremovals and oradditions, (i.e., changes in predator,
competitor, and prey abundances).
The locations of 15 potential study sites were obtained from commercial
bottomfishers who were activelyfishing thesebanks. Direction observations were made
on each site with the use ofthe mannedPisces/Fand Fsubmersibles and unmanned
RCV-150^OFoperatedby the Hawaii Undersea Research Laboratory (HURL). Funding
wasprovided for6, 8-hour submersible dives peryear andbetween 6 and 18, 2-hour
ROV dives peryearforatotal of3 years. The first set ofdives in 2001 was foran initial
survey ofall 15 sites. One study site was subsequently selected on eachbankwhere all
2002 and 2003 submersible dives were conducted.
During each submersible dive, counts ofall fish, invertebrates, andfishing debris
on the sites as well as size estimates forbottomfish species were obtainedusingtwo
techniques: four30-minute "contour" transects and two 30-minute bait stations. During
transects, two observers made independent identifications and counts fi-om each side
ofthe submersible. The length ofeach transect varied as aresult ofcurrent conditions
andbottom topography, but on average covered a distance of 1 km. Bait stations were
conducted in areas wheretargetedbottomfish species were seen duringtransects.At
each station, approximately 4.5 kg ofchopped squid andfishwas released nextto a 10-
cm diameter spherical markerused as a size reference. Afterthe bait and markerwere
deployed, the sub retreatedto a distance of5-10 meters and settled on the bottom with
its lights out. Bottomfish and otherpredatory species attractedto the bait were recorded
in ambient lighton a ROS 20/20Navigatorwide-angle CCD camera.A20-cm twin
laserscale attachedto the camera's pan andtiltprovided additional size data during
1
307
the stations. Afterthe dives, transect and bait station counts were extracted from the
videotapes, the latter being the maximum number offish caught on a single video irame
and/orrecorded by an observerat any one point in time. Bait station size measurements
were extracted from video still captures using Scion Image software.
In 2002, sets ofthree submersible dives using the same data-collecting protocol
were conducted on one otherbottomfishing site in the NWHICRER (Brooks Bank),
two sites on PenguinBank(PBl and PB2), which is a well-known bottomfishing area
in the MHI, and two sites in the Kahoolawe Island Reserve (KIR 1 and KIR 2), where
bottomfishinghas been prohibited since 1993. These sites provided comparative data for
WSR
interpretingthefindings from the Raitaand dives.
Statistical comparisons ofthe 2002 and 2003 transect and bait station counts
among sites were conducted according to the hypotheses shown in Table 1. Rankings (
beingthe highest expected mean counts/transect) werebased on presumedfishingactivity
at the different sites. Forexample, the two KIR sites were presumed to have the lowest
fishing activity andtherefore were expected to have the higherbottomfish counts (rank =
I), while the oppositewas expected forthe two Penguin Bank sites (rank= 3). Bycatch
analyses were carried out only onbait station counts ofnonbottomfish species. The
assumption was that species attracted to the bait and recorded at the stations were also
the most likely to be caught during commercial bottomfishing activities. Cnidarians and
nonprey invertebrate (i.e., sponges, urchins, and seastars) counts also were hypothesized
to be highest on the KIR sites and lowest on the PBI and PB2 sites, because oftheir
potential susceptibility to damage from fishing activities. Counts ofpotential prey and
competitor species were hypothesized tobe inverselyrelated to bottomfish counts.
Adultbottomfishtargetedbyfishers would have relatively few potential predators
besides medium to large sharks. Predators ofthis size are observed infrequently from the
submersible atbottomfish habitat depths, and therefore it was assumed that theirresponse
to bottomfish removals could not be evaluated.
Table I: Expected (i.e., hypothesized) countrankings foreach data categoryused in
comparing 2002 transect andbait station data obtained from each site. Numbers and
shadings are the expected ranks ofmean counts foreach category with 1 (dark shading)
beingthehighestand 3 (no shading) being the lowest. Bottomfish and bycatch counts
wereused in evaluating removal impacts; fishing gearand trash counts were used in
evaluating addition impacts; and counts ofcnidarians, other invertebrates, potential
competitor species, andpotentialprey species were used in evaluating alteration impacts.
The lastrow shows thepresumedfishing activity at each site. The expected rankings are
also shown in Tables 3-5 forreference.
Expected CountRankings Raita WSR KIR1 KIR2 PB1 PB2 Brooks
Bottomfish 2 2 1 3 3 2
'K
Bycatch 2 2 1 3 3 2
Fishing Gear 2 2 3 2
Trash 2 2 3 I 1jjjjll 2
Cnidarians 2 2 IHI 3 3 2
OtherInverts 2 2 3 3 2
Competitors 2 2 3 3 2
Prey 2 2 3 3 1 1 2
Presumed Fishing Activity med med low low high high med
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Counts fromtransects were first extrapolatedto a standard 1,000-m length,
yielding a 2-hectare sampling area (20 by 1,000 m). These hypotheses were tested
statisticallyusing software basedon the analytical methods described in Krebs (1999).
First, the data from each site were fittedto a negative binomial distribution to derive an
estimated mean, variance, and negative binomial exponent, k. Then the values foreach
site were used inboth U-tests andT-tests to determine theirapproximate goodness offit
to this type ofdistribution. Different sites were tested forequality followingthe method
ofWhite and Eberhardt (1980). The results ofthese tests are presented as one offour
models:
Model 1: the data from the tested sites have differentmeans and differentkvalues
Model 2: the data from the tested sites have differentmeans butthe same kvalues
Model 3: the data fromthe tested sites have the same means but differentk values
Model 4: the data from the tested sites have the same means and the same k
values
The analyses ofthe means were consideredto be mostrelevantto the hypotheses
above. Therefore, forthe purpose ofthis report, only models 1 and2 were considered
indicative ofa significant difference among the sites at P= 0.05.
Bait station size data onbottomfish species were normallydistributedand
analyzedby one-way analysis ofvariance (ANOVA) usingMinitab 12.1 software.
Similarto counts, average sizes were expectedto be inverselyrelated to the amount of
fishing activity onthe sites. It was hypothesizedthat the largestfish wouldbe found
onthe KIR siteswhile the smallest fishwouldbe foundonthe Penguin Bank sites. No
statistical analysis was attempted on ROVtransect records.
Commercialbottomfish andbycatch data from the Raita and "Rogatien"
WSR
(combined and St. Rogatien Banks) reporting grids were obtained for2001-2003
by Robert Moffitt from the National Oceanic andAtmosphericAdministration (NOAA)
fisheries database and were used as a secondmeans ofevaluating removal impacts in
these RPAs. Dueto limitations imposed on the length ofthis paper, onlythe mostrelevant
fishing data alongwith the submersible data obtained onbottomfish, fishing debris/trash,
and cnidarians are presented here. Forthose interested, a full-length version ofthe
original unpublished report fromthis study is available from the authors onrequest.
RESULTS
In Table 2, we provide 2001-2003 bottomfish catch andbycatch data forthe
Raitaand Rogatien grids. The values are the reported numberoffish caughtat each
location byyear. However, the listed locations may include awiderareathanjust
the nominal bank, e.g., adjacentbanks, pinnacles, and seamounts. On average, 2,017
bottomfish reportedly were removed fromthe Raita Bank area during each ofthe last
3 years. Onaga{Etelis cornscans) and uku accounted for44% ofthe catch followedby
hapuupuu {Epinephehis quernus), ehu {Etelis carbuncuhis), opakapaka {Pristipomoides
filamentosiis), gindai {Pristipomoideszonatus), butaguchi {Pseitdocaranxdentex), and
kalekale (Pristipomoidessieboldii).Areported 2,180 bottomfish wereremovedfromthe
Rogatien area. Overhalfofthe fish (51%) were opakapaka, followedby onaga, uku, ehu,
butaguchi, kalekale, gindai, andhapuupuu. On average, 214bycatch fishreportedly were
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caught in the Raita area each yearduring 2001-2003, and 138 bycatch fish were caught in
the Rogatien area. Ofthe six bycatch taxa, kahala {Seriola diimerili) was by farthe most
abundant species in the catch (93% and 88% forthe two areas, respectively).
Table 2: Raitaand St. Rogatien bottomfish catch andbycatch (# offish 2001-2003 data).
Raita StRogatien
Species 2001 2002 2003 mean/yr 2001 2002 2003 mean/yr
Pseudocaranxdentex 113 174 162 150 126 227 91 148
Eteliscarbunculus 304 195 132 210 199 114 187 167
Pristipomoideszonatus 93 313 89 165 31 95 66 64
Epinephelusquernus 264 370 262 299 51 113 21 62
Pristipomoidessieboldii 82 203 119 135 85 156 133 125
Eteliscoruscans 576 450 297 441 323 368 190 294
Pristipomoidesfilamentosus 173 259 99 177 1395 1089 839 1108
Aprionvirescens 221 84 1016 440 214 61 362 212
TotalBottomfish 1826 2048 2176 2017 2424 2223 1889 2180
Shark 2 0.7 3 2 1.7
Galeocerdocuvieri 1 0.3 0.0
Pontinusmacrocephalus 8 3 2 4.3 6 4 3.3
Caranxignobilis 9 17 8.7 36 12.0
Serioladumerili 142 326 131 199.7 177 94 92 121.0
Priacanthid 1 0.3 0.0
TotalBycatch 160 349 133 214 216 100 98 138
In2002 and 2003, all submersible dives were completed as planned which yielded
12 transects at each ofthe seven sites. With one exception (the KIR2 site, where five
bait stations were conducted), all submersible bait stations were completed as planned
whichyielded six per site. Asummary ofthe 2002 bottomfish, fishing/trash debris, and
cnidarian transect count data is presented in Table 3. The first row ofeach section ofthe
table shows the predicted ranking ofthe sites (different shadings) and whetherthey are
expectedtobe significantly different (+ or-). The remaining rows provide the mean and
standard errorofcounts, which were ranked and shaded forcomparison to the predicted
pattern, and indicate ifthe sites were significantly different at P<0.05. Data from sites
where countswere either or 1 for 12 transects, orwhere the variancewas equal to or
lowerthan themean (failed the assumptions ofanegativebinomial distribution) could
notbe tested (nt).
Ofthe 10 bottomfish species observed during submersible dives, only onaga and
ehu counts were significantly different among sites. PBl hadthe highest mean onaga
WSR
counts/hectare at26.7, while Raita (0.6) and (1.3) had the lowest. Raita had the
secondhighestcounts forhapuupuu. Forbottomfish in general, the mostnumberof
counts were obtainedirom the Kahoolawe and Brooks sites while the least numberof
counts were obtained from Raita and PB2 sites. While a few counts were made on lehi
(Aphareiis rutilans), uku, yellowtail kale (Pristipomoides aiiricilla), andbutaguchi,
these species were not adequately sampled in this study, as a result ofthe transects
being generallybelow their optimal depth. Between 2002 and 2003, there was a
significant decrease in onaga, ehu, andkalekale counts at Raita Bank (Kelley and Moffitt,
unpublishedreport).AtWSRBankhowever, unlike Raita, the difference was only
significant forkalekale. Ingeneral, bottomfish counts atbothbanks decreased between
2002 and2003.
310
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As expected, the total amount offishing debris was significantly higheron PBI
and PB2 in comparison to other sites. However, Raita had the lowest level ofall seven
sites including KIRl and KIR2, while WSR and Brooks had intermediate levels as
expected. Fishing lines, ratherthan anchors, anchorchains, orfishing weights, were ihc
majortype oflost gear. Overall, trash counts were low with KlRl and KIR2 topping the
list at 0.5 and 1.4 items/hectare, respectively. Metal and cloth debris resulting from past
military activities offKahoolawe accounted forthe majority ofitems seen. Raita and
PBI had the lowest levels oftrash counts, both ofwhich had 0.1 items/hectare. Neither
fishing debris nortrash appeared to be significant problems on any ofthe seven sites in
2002; also there was no change in the amount offishing debris ortrash on Raita between
2002 and 2003 (Kelley and Moffitt, unpublished report). Bottomfishing debrisperse was
rarely encountered and did not significantly increase on eitherbank.
Withrespectto alteration impacts, 64 different cnidarians were counted which
were grouped into seven categories: Actinarian-like (anemones, corallimorpharians, and
ceriantharians),Alcyonacean-like (soft corals andtubularid hydrozoans),Antipatharians
(black corals and "bushy" hydrozoans), Gorgonians (gorgonians and zoantharians
that grow on gorgonians), Pennatulaceans (sea pens), Scleractinians (hard corals),
and unidentified cnidarians that couldnotbe assignedto one ofthe other six groups.
Significant differences among sites werepresent in all seven categories as well as the
total numbers ofcnidarians. Ofparticular interestwere the low counts at Raita, WSR, and
PB2 (28-41/hectare) in comparison to the other sites (153-2,350/hectare). KIRl and KIR2
had the highest total cnidarian counts due to high numbers ofgorgonians (263-1,190/
hectare) and scleractinians (242-1,116/hectare). Antipatharians and alcyonaceans were the
onlytwo groups on Raita and WSRwith moderate numbers in comparison to the other
sites.
Tables 4a and4b summarize the bottomfish andbycatch bait station counts from
WSR
each site. Mirroring the results from transects, Raita and generally had the lowest
meannumber ofbottomfish perstation. Raita hapuupuu andWSRkalekale were the two
exceptions, althoughneitherwas significantly higherthan othersites. Similarto transect
data, the PBI and KIRl sites hadthe highest onaga counts, followedby Brooks. Between
2002 and 2003, mean onagabait station counts decreased on both Raita and WSR,
although the difference on the latterwas not significant. Consistentwith commercial
catch data, kahala were the predominant"bycatch" species observed at bait stations. Two
Seriola species were observed at a numberofthe stations (S. dumeriU and S. hvoUana),
which were notalways easyto differentiate. Therefore, the data on these species were
combined inTable4b asSeriolasp.
Bait station size data arepresented inTable 5. Size data from the Brooks site
were not available forthe preparation ofthis report. With the exception ofone extremely
large individual at PB2 (FL= 99 cm), Raita Bank had the largest sized onaga (mean =
65.3 cm FL, n = 30), ehu (mean = 44.5 cm FL, n = 16) and hapuupuu (77.7 cm FL, n=
19). In contrast, WSRhadthe smallestonaga (mean= 49.3 cm FL, n = 39) as well as
the smallest ehu (34.3 cm FL, n = 8) ofthe six sites shown. Gindai were the only other
species ofwhich measurements were made at more than two sites. WSR had the second
largestindividuals (mean = 36.3 cm FL, n = 8) afterPBI (mean = 36.8 cm FL, n = 10). In
general, size measurements did not follow the expectedpattern among sites. Furthermore,
WSR
2003 Raita and size datadidnot follow the expectedpattern either.
312
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DISCUSSION
All types offishingmethods lead to removal impacts. Methods are considered
selective when they yield ahigh percentage oftarget versus bycatch species in the catch.
Differentmethods also have varyingpotential foraddition and alteration impacts. Bottom
trawling is the subject ofthe largestnumberofreports onfishing impacts overthe last 3
years (Rester, 2003). Bottom trawling generally causes substantial removal impacts with
low selectivity (high levels ofbycatch); can cause dramatic alterations to the benthic
habitat andcommunity (particularly cnidarians and other sessilebenthic invertebrates);
and when lost can contribute heavily to the addition offishing debris. Trap fishing is
more selective than trawling, but canproduce moderate levels ofaddition and alteration
impacts. In contrast, hook-and-line methods (including trolling, longline, and handline
fishing) are consideredto be "low impact" (Morgan and Chuenpagdee, 2003). Longline
fishing hasbeen shownto alterprey and competitorpopulations inpelagic ecosystems
(Ward and Myers, inpress); however, trolling and handline fishing are relatively selective
and are not consideredto have major impacts. Bottomfishing (a forai ofhandlinefishing)
andtrolling are the onlytypes offishingpermitted on Raita andWSR Banks.
Commercial catch data from 2001-2003 indicated that on average, over2,000
bottomfish are beingremoved from each ofthe Raita and St. Rogatien reporting gridsper
year. The estimated maximum sustainable yields (MSY) are reported as 16.9 and 11.7 mt,
respectively (WPRFMC, 1986). Ifthe meanfish weight is assumedto be 4.5 kg, thetake
onthese banks isjustbelow MSY. Unfortunately, due to poor spatial resolution ofthe
reporting grids, it is notknown exactly how many fish are removedannually from each of
the two RPAs. This is aparticularproblem forthe St. Rogatien grid data which includes
boththe WSR as well as the larger St. Rogatien Bank.Above the 100-fathomcontour, the
WSR
calculated areas ofRaita, and St. Rogatien are 570, 54, and 484 km-, respectively.
The combined area ofthe lattertwo is 538 km-, orapproximately the same as Raita,
which maybe whythe catches from these two grids are similar. However, the extentof
suitablebottomfishhabitat on each ofthe banks has notbeen determined.
Fishing undoubtedlyhas a significant effect onthe abundance andmean fish size
oftargeted species fromthese andotherareas throughoutthe HawaiianArchipelago.
Perhaps the more important question is whetherthe sustainability ofthe populations on
these banks is being impactedbythis activity. As Table 2 shows, landings ofonaga and
opakapakagenerally decreased while landings ofuku generally increased during the 3-
year studyperiod. Both changes were most likely due to a shift in fishing effort. Either
an increase inuku catchability (previously reported several times fortheNWHI fishery)
oradecrease in onaga and opakapaka catchability could havebeenthe cause ofthis
pattern. These data are difficult, ifnot impossible, to interpretwithoutknowing the effort
expendedtargeting each species during thatperiod.
In 2002, the numberofonaga counted from the submersible atboth Raita and
WSR
were significantly lowerthan atthe otherfive study sites (Kelley and Moffitt,
unpublished report). Comparison between the 2002 and 2003 data also supports the
possibilitythat onaga abundance is decreasing atthe two sites as well. Opakapaka
observations were too low to be statisticallytested, but it should be notedthatthey