Total Bycatch Research Articles

Spatial variation in by-catch from a prawn seine-net fishery in a south-east Australian coastal lagoon

Observer-based estimates of the catches and by-catches from prawn seining (locally termed ‘snigging’) in Tuggerah Lake (NSW, Australia) during the 1998/99 fishing season are presented. Observed catches included three species of penaeid prawns, while observed by-catches contained a total of 49 finfish and 5 invertebrate taxa. The overall by-catch:prawn catch ratio by weight was 0.9:1, and in catching an estimated 20 ± 4 t of prawns the fleet took an estimated total by-catch of ± 2 t throughout the 6-month fishing season. The by-catch included large numbers of small (<15 cm total length) finfish species important in other commercial and recreational fisheries, including Gerres subfasciatus,Rhabdosargus sarba and Acanthopagrus australis, as well as several small demersal species of little economic value. Multivariate analyses indicated that by-catch composition differed between seines taken over shallow seagrass and bare substrata, with catch rates of several species being greater over seagrass. It is recommended that strategies to reduce potential ecological impacts and by-catch in this fishery be investigated, including fixed spatial closures over seagrasses and the development of alternative fishing gears and practices.

Analysis of Minimum Size Limit for the Red King Crab Fishery in Bristol Bay, Alaska

Abstract Low stock status of red king crabs Paralithodes camtschaticus in Bristol Bay prompted an industry initiative to reduce the minimum size limit for the commercial fishery from 165 mm in carapace width (CW) to 152 mm in CW. In terms of carapace length (CL), which is the metric used in data collection programs, this is equivalent to a reduction from 137 to 128 mm CL. The rationale was primarily to reduce potential nontarget handling mortality, which was suspected to contribute to the depressed stock status. Analysis of red king crab fishery observer data showed that the reduced size limit would initially increase catch rates of legals (under new size limit) by 10–41%, diminish total bycatch of nontarget red king crabs (sublegal and female crabs) by 9–33%, and reduce the fishing effort (pot lifts) needed to attain annual catch quotas by 2–27%. Yield-per-recruit analysis indicated that steady-state yield would decline 5–7% under the smaller size limit, assuming a 20% handling mortality rate. Size distr...

Bycatch and discards of the Kuwait shrimp fishery

The landings and survey data for the Kuwait shrimp fishery were analyzed. The estimated bycatch-to-shrimp ratios exhibited a seasonal pattern, with summer having the highest ratio. There was a significant difference in bycatch-to-shrimp ratio between Kuwait Bay and the rest of the Kuwaiti waters. The temporal and spatial patterns of the ratio strongly support the seasonal and area closures implemented for the shrimp fishery in terms of bycatch reduction. The bycatch-to-shrimp ratio of the shrimp fishery was 15.32, 6.78 and 13.68 in 1987/1988, 1988/1989 and 1989/1990, respectively. Total bycatch in the shrimp trawling ranged from 34 740 to 55 500 tonnes (t) during the study period, and more than 98% of the bycatch was discarded at sea. The total discards from the shrimp fishery was 7.5-fold higher than the mean of annual finfish landings in Kuwait. The major part of the discarded was non-Ariid finfish, accounting to 53.61%.

Performance of a bycatch reduction device in the shrimp fishery of the Gulf of California, México

Although shrimp fisheries are of great economic importance worldwide, they produce serious ecological disturbances and affect other resource harvesting activities such as small-scale fisheries. We tested performance of the Square Mesh/Extended Funnel bycatch reduction device (BRD) in the bottom trawl shrimp fishery of the Gulf of California. Efficiency of the BRD was determined under controlled conditions in terms of exclusion rate of fish bycatch, shrimp-capture loss and exclusion of certain fish species selected as indicators. Average exclusion rate for finfish species was 37% and that for shrimp, 7%. Total bycatch was decreased by 40% in comparison to the control trawl (no BRD). Extrapolation of this result to the entire commercial fleet suggests that BRD use would allow the exclusion of 73 thousand tons of bycatch per year in the Gulf. Their use would also help the recovery of certain endangered species, such as Totoaba macdonaldi. For this endemic fish, the exclusion rate of juveniles in our trials was 81%. An economic analysis showed that with a shrimp-capture loss of 7%, an average shrimp boat will continue to realize profits, but that opportunity costs could make this type of shrimping financially unattractive.

Bycatches of harbour porpoises (Phocoena phocoena L.) in Danish set-net fisheries

Data on bycatch of harbour porpoise (Phocoena phocoena L.) in the commercial Danish set-net fisheries were sampled from 5,591km nets in the period 1992 to 1998 using independent observers. A total bycatch of 325 harbour porpoises was reported. Cluster analysis was used to stratify the sampled fishing trips and official catch statistics into a number of different m6tiers defined by the target species for the trips. Extrapolation of the observed bycatch rate to total fish landings of the Danish set-net fleet gave an average annual bycatch of 6,785 (CV 0.12) for the North Sea fisheries in the period 1994-1998. Sampling was not sufficient to estimate total bycatch for other areas. Bycatch was observed in Kattegat but not in the Baltic Sea. Generalised Linear Models were used to identify significant factors for bycatch in the North Sea. The bycatch rate, given as number per length of nets x soak time, was significantly lower in fisheries for flatfish compared to roundfish fisheries. The highest bycatch rate was in the cod fishery over wrecks and no bycatch was observed in the sole fishery. Significant seasonal variation of bycatch was identified with the highest bycatch rate in the first and third quarter of the year. Bycatch rates had not changed in the observed period and there was no significant difference in bycatch rates between sub-areas.

Harbour porpoise (Phocoena phocoenaL.) by-catch in set gillnets in the Celtic Sea

A programme to assess the cetacean by-catch in the Irish and UK set gillnet fisheries in the Celtic Sea was conducted from August 1992 to March 1994 using volunteer observers. Observers were present for the hauling of over 2500 km of net which caught 43 harbour porpoises and four common dolphins, with one of each alive. The by-catch rate was 7.7 porpoises per 10 000 km · h of net immersion. A negative relationship was found between porpoise by-catch and tidal speed but no other relationships were found with operational or environmental variables. Spatial and temporal stratification of the by-catch rate and eVort data had a small eVect on estimated total by-catch, which was therefore estimated from pooled data. The estimated total annual by-catch of 2200 porpoises (95% C.I. 900‐3500) is 6.2% of the estimated number of porpoises in the Celtic Sea and there is serious cause for concern about the ability of the population to which they belong to sustain this level of by-catch. ? 1997 International Council for the Exploration of the Sea

By-catch of Albatrosses and other Seabirds by Japanese Longline Fishing Vessels in the Australian Fishing Zone from April 1992 to March 1995

SummaryData collected by Australian observers, combined with logbook data supplied by all Japanese vessels fishing in the Australian Fishing Zone were used to estimate the total seabird catch and catch rates (and associated variances) within the Australian Fishing Zone by season and area. The species composition of sub-samples of captured seabirds was used in conjunction with the estimates of total by-catch to provide estimates of by-catch by species. The total by-catch of all seabird species by Japanese longline within Australian waters was estimated to be 2981 (coefficient of variation [cv] 17%) for the 1992 fishing year, 3590 (cv 15%) in 1993 and 2817 (cv 19%) in 1994. Because these estimates are based on birds observed hauled on board, they underestimate the total number of seabirds killed by fishing operations. The increase in total seabird by-catch between 1992 and 1993 is partly due to the use of monofilament nylon longline gear by two vessels in 1993, and the decrease from 1993 to 1994 was mainly due to a corresponding reduction in fishing effort. For the three years examined, 78% of the total seabird by-catch was albatrosses, with Black-browed Albatross Diomedea melanophrys and Shy Albatross D. cauta caught in the greatest numbers. Catches of Yellow-nosed Albatross (D. chlororhynchos), Wandering Albatross D. exulans and Grey-headed Albatross D. chrysostoma were also significant. The proportions of individual species caught showed considerable inter-annual variability.

A review of the offshore trawl fishery for crustaceans on the east coast of South Africa

This paper reviews current knowledge on the trawl fishery for crustaceans on the east coast of South Africa. The shallow water fishery targets penaeid prawns, particularly Penaeus indicus Milne‐Edwards, while the deep water fishery targets pink prawns, Haliporoides triarthrus Stebbing, langoustines, Metanephrops mozambicus (Jenkins), and rock lobster, Palinurus delagoae, Barnard. Between 1988 and 1993, annual catches of targeted species averaged about 350 t. There was a total bycatch of about 1700 t per annum, most of which was discarded. Retained bycatch was dominated by the red crab, Chaceon macphersoni, as well as fish and cephalopods. Although trawling effort declined during the period under review, this trend has recently reversed.

By-catch of an Australian stow net fishery for school prawns ( Metapenaeus macleayi)

The by-catch of the Clarence River stow net fishery during the 1991–1992 and 1992–1993 fishing seasons was comparatively small and dominated by small fish of no monetary value. The number offish caught by the fleet per dig-night (the basic unit of fishing effort) was 1011 ± 297. Of this number, 59.5 ± 20.0 were individuals of species of commercial or recreational importance. Estimates of the total by-catch for the fleet were dominated by exceptionally large catches, particularly during the lunar month beginning in November 1991. These exceptional catches produced imprecise estimates of total by-catch for the 1991/1992 fishing season. The impact of stow netting on coexisting fisheries was small. An estimated 1144 of the 67 231 bream caught by stow netting during the study would have survived to the minimum legal size for this species. We conclude that, although stow netting had comparatively little impact on other fisheries for finfish during our study, there exists the potential for very large catches and greater impacts. These large catches appear to be associated with increases in river discharge.

Consumer/Professional

The by-catch of the Clarence River stow net fishery during the 1991–1992 and 1992–1993 fishing seasons was comparatively small and dominated by small fish of no monetary value. The number offish caught by the fleet per dig-night (the basic unit of fishing effort) was 1011 ± 297. Of this number, 59.5 ± 20.0 were individuals of species of commercial or recreational importance. Estimates of the total by-catch for the fleet were dominated by exceptionally large catches, particularly during the lunar month beginning in November 1991. These exceptional catches produced imprecise estimates of total by-catch for the 1991/1992 fishing season. The impact of stow netting on coexisting fisheries was small. An estimated 1144 of the 67 231 bream caught by stow netting during the study would have survived to the minimum legal size for this species. We conclude that, although stow netting had comparatively little impact on other fisheries for finfish during our study, there exists the potential for very large catches and greater impacts. These large catches appear to be associated with increases in river discharge.

Feeding ecology of the piscivorous birds Phalacrocorax varius, P. melanoleucos and Sterna bergii in Moreton Bay, Australia: diets and dependence on trawler discards

The diets of three piscivorous bird species from Moreton Bay, Queensland, Australia, were monitored for 14 mo from April 1986 to September 1987. Regurgitated pellets from Phalacrocorax varius (pied cormorant), P. melanoleucos (little pied cormorant) and Sterna bergii (crested tern) were collected monthly and prey items were identified from otoliths, spines and whole-fish remains. Otolith weight to fish length and weight relationships were used to aid in calculation of diet composition. Sepia sp. was the commonest prey of P. varius and P. melanoleucos; Sterna bergii took few Sepia sp. In order of decreasing importance, the teleosts Sillago maculata, Apogon fasciatus and Leiognathus moretoniensis were the next most common prey in all diets. P. melanoleucos has previously been reported to eat primarily crustaceans. The size ranges of fish prey were 18 to 452 mm for P. varius; 25 to 246 mm for P. melanoleucos; and 33 to 226 mm for Serrna bergii. The three species had similarly narrow diets. There was a significant rank correlation between the diet of P. varius and the by-catch of the prawn trawlers. This, together with observations of feeding behaviour, the similarity of the diets and the benthic and benthopelagic nature of most prey species, suggests that in Moreton Bay the three bird species are primarily dependent on food from fishery discards. The population of about 350 P. varius possibly consumes 13.7% of the total fish by-catch. The relationships between the fishery and the piscivorous birds in discussed in relation to size of bird populations and its possible dependence on the fishery.