Dipnet Fishery Research Articles

Effect of Diversity of Fish Landings on Sorting Time in Stick-held Dip Net Fishery

Effect of Diversity of Fish Landings on Sorting Time in Stick-held Dip Net Fishery

Evaluation of the influence of spatial treatments on catch-per-unit-effort standardization: A fishery application and simulation study of Pacific saury in the Northwestern Pacific Ocean

Fishery-dependent catch-per-unit-effort (CPUE) data often exhibit spatial heterogeneity over space and time, which means that the spatial treatment in statistical models used to standardize CPUE is critically important. We evaluated several spatial treatments to standardize CPUE data using Generalized Linear Mixed Models (GLMMs). Results include a real-world application and a simulation based on the Taiwanese stick-held dip net fishery for Pacific saury in the Northwestern Pacific Ocean. We compared the performance of three spatially stratified approaches in GLMMs, (i) Ad hoc; (ii) Binary (binary recursive area partitioning based on model selection criteria); and (iii) Spatial clustering (partitioning of grids into discrete strata based on the spatial proximity and average CPUE in each grid), to a spatio-temporal GLMM (VAST). An influence analysis was constructed to quantify discrepancies between unstandardized and standardized indices that assisted in identifying the annual influence of explanatory variables in GLMMs. We developed a simulation to corroborate the results from the case study and evaluated the four spatial treatments using data generated from two contrasted, random and preferential, sampling scenarios. Results from the real-world application indicated that VAST was statistically superior to the other approaches, based on conditional deviance explained, conditional Akaike Information Criterion, and five-fold cross-validations. The influence analysis indicated that the interaction of year and spatial effect or spatio-temporal variable had a major influence on the standardized CPUE. Both simulation scenarios showed that VAST performed the best, with the lowest model error (measured by root mean square error) and bias, for estimating relative abundance indices. Although the spatial clustering approach created a flexible shape for the area strata, the simulation results under preferential samplings showed that clustering with a stronger emphasis placed on average CPUE could lead to bias in estimated abundance indices. However, spatial clustering that balanced average CPUE with spatial proximity could be a reasonable alternative if it is not possible to apply a spatio-temporal approach. The importance of conducting influence analysis and the greater performance of a spatio-temporal approach are highlighted.

Studying Kenai River Fisheries’ Social-Ecological Drivers Using a Holistic Fisheries Agent-Based Model: Implications for Policy and Adaptive Capacity

Alaska’s salmon fisheries are one of the more intensely managed natural resources in the world. The state’s salmon fisheries support recreational, subsistence, and commercial harvest with multiple billions of dollars flowing into the economy, and define the cultural identity of many Alaskans. Fishery management practices rely on historic records to set policies with two goals: to meet salmon escapement quota and to maximize salmon harvest. At the same time, rapid social and ecological changes to the sub-Arctic are already impacting salmon runs and fisheries management. Combined with the inability of fishery managers to test the outcome of proposed policy changes, an understanding of the role social and ecological drivers play in harvest and effort is required. To address the two-forked problem of understanding socio-ecological dynamics and potential policy responses to ecological and social changes, we (1) conducted stakeholder workshops to solicit key system drivers, (2) built an integrated agent based model (ABM) of the system’s socio-ecological dynamics, and (3) tested the impacts of alternative future scenarios of ecological, social, and policy changes on the system’s outcomes. We previously constructed and validated a high-fidelity, data-driven, agent-based model of the Kenai River, Alaska that simulates seasonal harvest of sockeye and Chinook salmon, the fishing activities of the personal use fishery, commercial drift, and set gillnet agents. We study the role of key stakeholder and ecological drivers, using the ABM decision support tool, and their implications for fisheries management policies. Analysis of the scenario based studies found resilience in management of commercial fisheries to changing salmon migration dynamics, a lack of adaptive capacity in recreational (personal use) dipnet users to altered sockeye salmon runs, and the possible utility of introducing management measures in the dipnet fishery to manipulate sockeye escapement levels. These findings represent the usefulness of this type of ABM in assisting fishery managers everywhere in investigating possible future outcomes of different management or ecological scenarios.

An adaptable agent-based model for guiding multi-species Pacific salmon fisheries management within a SES framework

Informing fishery management decisions using coupled socio-ecological systems (CSES) models requires model construction that captures the systems interactions with high precision. Ecological uncertainty in fishery models is easily reduced using existing scientific literature, but social drivers are often poorly defined or understood. The lack of knowledge about fishermen behavior results in inaccurate models of questionable utility for fishery managers. We designed and constructed a high fidelity agent based model (ABM) using the socio-ecological framework that reduces social system uncertainty by capturing complex behaviors using data-driven bounded rationality and feedback. The resulting generalized ABM of CSES dynamics was instantiated to Pacific salmon fisheries at Kenai river in Upper Cook Inlet, Alaska. The data-driven model construction fuses multiple data-sets for classification of social and ecological fishery regimes into stochastic distributions; the agent behaviors were generalized by evolving parametrized equations using data-driven machine learning; multiple non-trivial metrics on multiple scales verified model's accuracy and predictive capacity. The verified model of CSES dynamics at the Kenai river revealed recent instability in the dipnet fishery coupled dynamics, historic instability in the drift gillnet fishery coupled dynamics due to a compensatory and aggressive fishing strategy, and in the future the model will be used for scenario-based studies to understand the outcomes of alternative management strategies.

Evaluating the technical efficiencies of fishing vessels to achieve effective management of overexploited fisheries

Global marine capture fisheries are undergoing serious stress, with overfishing as one of the major problems. In order to mitigate the overexploitation of capture fisheries, government regulation or fisheries management is necessary. Among various management approaches, vessel quantity control is being widely employed. To achieve effective governance of fisheries, the technical efficiency (TE) issue needs to be considered in the implementation of vessel quantity control. Using the Pacific saury (Cololabis saira) stick-held dip net fishery in Japan as a case study, this paper estimated the TE of sampled fishing vessels and explored the possible factors affecting the gap in efficiency. This paper aims to provide suggestions for a better implementation of vessel quantity control in global Pacific saury fishery, and also to serve as an empirical example of integrating TE analysis into management of overexploited fisheries for achieving satisfactory effects. Results show the TE score of the sampled fishery averaged around 0.7 from 2009 to 2014, and factors concerning owners/skippers’ motivation such as vessel ownership and specialization, vessel tonnage as well as skippers’ age show positive effects on the TE. Our findings in the present work provide important strategies for mitigating overexploitation in fisheries. Conducting technical efficiency analysis of targeted fisheries is a vital issue to be considered for designing and realizing an effective implementation of fisheries management approaches. The large vessels and the enthusiasm of vessel owners/skippers need to be particularly addressed when vessel quantity limit is considered to mitigate the problem of overfishing.

Sea surface temperature fronts affect distribution of Pacific saury (Cololabis saira) in the Northwestern Pacific Ocean

Pacific saury (Cololabis saira) is an important fisheries resource and commercial species of Taiwanese deep-sea saury stick-held dip net fishery in the Northwestern Pacific Ocean. In this study, the logbook data of a 3-year (2006–2008) Taiwanese Pacific saury fishery and corresponding satellite-derived MODIS sea surface temperature (SST) data were analyzed to detect SST fronts and examine their influence on the spatio-temporal distribution of Pacific saury. The fronts were identified by the Cayula–Cornillon single-image edge detection algorithm. The results show that low frequency of SST fronts is associated with lower CPUEs during the early fishing season (June–August), while high frequency of SST fronts is associated with higher CPUEs during the peak fishing season. When fishing locations of Pacific saury are close to the SST fronts, higher CPUEs are observed. Results of this study provide a better understanding of how SST fronts influence distribution of Pacific saury and improve the basis of fishing ground forecasting.

꽁치봉수망어업에 있어서 달빛이 어획에 미치는 영향

In order to investigate influence of moon light to the fishing of Pacific saury stick-held dip net fishery in the northwestern Pacific Ocean, casting number, catch and CPUE were analyzed between the full moon and the new moon phases. Based on analyses of data taken from 8 vessels during 1992~2002, casting numbers at the full moon phase and the new moon phase were 110.3 and 121.0 times, respectively, and the first was lower than the latter by 8.8%. Catches of the full moon phase were higher than the new moon phase by 12.5% and CPUE expressed in ton/day and ton/haul were also higher by 31.5%, 26.1% respectively.

북태평양 한국 꽁치봉수망어엽의 현황 분석

북태평양에서 조업하는 우리나라 꽁치봉수망어업의 어획량과 시기별 어장 중심 및 어획적수온 등을 검토하고 조업시 소나 사용에 따른 어획 효과를 분석하였다. 조업 시기는 5~12월이었고 어획 비율과 CPUE 측면에서 볼 때, 한<TEX>${\cdot}$</TEX>일 어업협정 발효 이전인 1985~1998년의 주어기는 9~11월로, 발효 이후인 1999~2002년의 주어기는 8~10월로 추정되었다. 한<TEX>${\cdot}$</TEX>일 어업협정 이후 어장 중심은 일본 동쪽 연안 측으로부터 러시아 남쿠릴열도 동쪽인 43<TEX>$^{\circ}$</TEX>N 와 151<TEX>$^{\circ}$</TEX>E 부근으로 이동하였다. 꽁치의 어획적수온은 5월에는 12.5~14.4<TEX>$^{\circ}C$</TEX>, 6월은 12.0~14.2<TEX>$^{\circ}C$</TEX>, 7월은 11.4~13.9<TEX>$^{\circ}C$</TEX>, 8월은 11.4~15.9<TEX>$^{\circ}C$</TEX>, 9월은 12.9~16.9<TEX>$^{\circ}C$</TEX>, 10월은 12.7~l7.3<TEX>$^{\circ}C$</TEX>, 11월은 13.1~17.6<TEX>$^{\circ}C$</TEX> 그리고 12월에는 15.0~19.1<TEX>$^{\circ}C$</TEX>이었다. 어획종은 총 13종으로서 목표종인 꽁치가 99.9% 어획되어 대부분을 차지하였다. 조업일수는 소나를 보유한 조업선과 소나를 보유 하지 않은 조업선 사이에 뚜렷한 차이를 나타내지 않았으나 투망횟수, 어획량 및 CPUE는 소나를 보유한 조업선이 각각 13%, 26%, 12% 높게 나타났다. This paper presents a general overview of the Korean stick-held dip net fishery for Pacific saury operated in the North Pacific Ocean since 1985. Annual catches, annual centroids distribution of fishing ground, and optimum fishing temperatures were compared between the periods before and after the new Korea-Japan bilateral fishery arrangement established in 1998. Fishing usually began in May and ended by December, during which major catches were taken in the months September~November before the bilateral fishery arrangement between Korea and Japan, whereas in August~October after the arrangement. It was observed that after the arrangement the centroids of fishing ground was shifted from the usual fishing area off the east coast of Japan to the east of South Kuril Islands, 45<TEX>$^{\circ}$</TEX>N and 151<TEX>$^{\circ}$</TEX>E. Optimum fishing temperatures appeared to be different by month ; 12.5~14.4<TEX>$^{\circ}C$</TEX> in May, 12.0~14.2<TEX>$^{\circ}C$</TEX> in June, 11.4~13.9<TEX>$^{\circ}C$</TEX> in July, 11.4~15.9<TEX>$^{\circ}C$</TEX> in August, 12.9~16.9<TEX>$^{\circ}C$</TEX> in September, 12.7~17.3<TEX>$^{\circ}C$</TEX> in October, 13.1~17.6<TEX>$^{\circ}C$</TEX> in November, and 15.0~19.1<TEX>$^{\circ}C$</TEX> in December. A total of 13 species were caught during scientific observation periods but the target species, Pacific saury, accounted for about 99.9% of the total catch. Although there was no difference in fishing days between those vessels equipped with the sonar and those without sonar, number of set, total catch, and CPUE of those with sonar were higher than those without sonar by 13%, 26%, and 12%, respectively.

Scavenging on discarded saury by demersal fishes off Sendai Bay, northern Japan

Pacific saury Cololabis saira were found in 24 out of 1314 stomachs of demersal fishes collected by bottom trawling at 245–393 m depths. The same area was occupied by the stick‐held dipnet fishery for saury, in which a landing limitation was enforced to avoid overfishing. The fish species containing saury were: Pacific cod Gadus macrocephalus, walleye pollock Theragra chalcogramma, and oilfish Ruvettus pretiosus. These demersal species would not encounter living saury naturally, which normally are distributed above thermoclines. The ingested saury were smaller than market size which suggests that the saury from fish stomachs were discarded by fishermen because of small sizes to maximize profits under the landing limitation.The scavenged saury made up 41.5, 24.6 and 77.7% of the diets of large‐sized (&gt;30cm)Pacific cod, walleye pollock and oilfish, respectively in terms of DW composition. The extent to which discarded saury contributed to the total diet in the demersal fish assemblage, calculated by considering species composition and diets of bottom fishes, was 21.8% of the total diet. The discarded saury seemed to compensate the less productive feeding environment during autumn for the bottom fishes.

Effects of a Recreational Dip-Net Fishery on Rainbow Smelt Egg Deposition

We sampled egg deposition in three Lake Huron tributaries to measure the effect of recreational dip-net activity on egg deposition by spawning rainbow smelt Osmerus mordax. We compared egg densities sampled nightly at paired sites, one of which was protected from fishing activity. We found that sites protected from the recreational fishery had significantly higher mean egg densities than sites that were vulnerable to disturbance by fishing activities (wading, net contact). When recreational fishing activity was absent, we found no significant difference in egg densities between paired sites, which indicated that our protection devices did not influence egg deposition. We found that the higher the level of recreational fishing effort (people/100 m2), the greater the decline in egg densities in unprotected sites (r2 = 0.63). Our results indicate that net abrasion and wading associated with recreational dip-net fisheries can significantly reduce egg density and that this reduction may limit reproductive success in areas where spawning habitat is limited and recreational fishing effort is intense. In aquatic systems where tributary recruitment of rainbow smelt is significantly affected by recreational fishing activity, regulations limiting effort or providing spawning refuges may be warranted.

Impact factors of purse seine net and dip net fisheries on a chub mackerel population

There are two major kinds of fisheries for the chub mackerel in Japan. The purse seine net fishery exploits young and adult fish during the foraging season, while the dip net fishery exploits fish before and during the spawning season. To compare the damage to the chub mackerel stock caused by purse seine net and dip net fisheries, we introduced impact factors of the two kinds of fisheries on the two kinds of fisheries and estimated number of eggs spawned in 1982. We defined the impact factor as the ratio of the average reproductive value of individuals caught by each fishery to the reproductive value at maturity. The number of individuals caught by the purse seine net fishery was 66 times larger than the number caught by the dip net fishery, while the impact factor of the former was 84% of that of the latter. Thus, the total damage caused by the purse seine net fishery was much higher than the damage caused by the dip net fishery. We can evaluate the damage caused by mortality factors on endangered species using this method.

Population Dynamics of Anadromous Rainbow Smelt Osmerus mordax, in a Massachusetts River System

Population dynamics of anadromous rainbow smelt, Osmerus mordax (Mitchill), in the Parker River estuary, Massachusetts, were investigated during the spring spawning runs of 1974 and 1975, and the winter recreational fishery of 1974-1975. Growth (in length) was greatest in the first year of life, and nearly ceased by age V. Avon Bertalanffy growth function fitted to the data (l = total length, mm; t = years) is: lt = 256.29[1 - e−0.6393(t + 0.0018)]. The length (L, total length, mm)/weight (W, g) regression is: log10W = −6.0315 + 3.3592 log10L. Parker River fish were partially recruited to the spawning population at age I and were probably fully recruited at age II. Total mortality was lower for females than males. Total annual mortality of adults averaged 72%. Fifty percent selection to the angling fishery occurred at 166 mm. Modeled values of fishing mortality that result in greatest yield per recruit to both the present angling fishery and a simulated dipnet fishery on the spawning grounds would probably be detrimental to future recruitment.

FISHERY ON THE COAST OF THE SEA OF OKHOTSK

The region that is contiguous to the Sea of Okhotsk in Hokkaido is a tract of land covering Cape Notsuke, by way of Cape Shiretoko to Cape Soya. In this thesis, however, Wakkanai is also included. There lie three cities, nine towns, and three villages in this region, and about 5, 000 families of fishermen are living depending upon the Sea. 1. STATIONARY FISHING: Salmon and trout fisheries are done in this method, which excel in Shari and in Shibetsu. Especially the fishermen of Utoro in Shari depend upon this stationary fishing, and in the fishing season they move, to Shiretoko Peninsula, to the north of Utoro, to fish. 2. CO-OPERATION FISHING: This is cheifly practised in gathered tangle and catching hairy-crab. The tangle is called Rishiri tangle, and is grown on the rocky shore of Wakkanai and Rausu. As the fishing season approches, in Rausu they move to the northern part of Shiretoko Peninsula hairy-crab pot fishery is practised on a huge continental shelf lying in front of the coast from Tokoro to Hamatombetsu. Omu, Esashi, and Mombetsu excel in their catch because of their convenient location. 3. PERMISSION FISHERY: In this, scallop dredge fishery, saury stick-held dip net fishery, one-boat medium trawl fishery, dog fish drift line fishery are chiefly included. The fishing-places of scllops are the continental shelf off the coast of Kitami and C. Notsuke and its cheif producting districts are Yubetsu, Tokoro, Abashiri, and Esashi. The cheif fishing place of saury stick-held dip net fishery is the offing Mombetsu, and the fishermen sail out fishing from Abashiri and Mombetsu as thier bases. Fishing season being late, the fleets of vessels belonging to the Pacific Ocean also take part in it. One-boat medium trawl fishery is done to catch pollacks, cod, lockingtons, sharks on the huge continental shelf covering off the coast of Tokoro to Sakhalin, and their bases are Abashiri, Mombetsu, Esashi, and Wakkanai. Abashiri and Tokoro excel in dog fish drift line fishery and its fishing-places are near the isobathyic line of 200 metres. But in late autumn sharks being near thes hore and living on the bottom of the sea, they fish with one boat medium trawl fishery. 4. SECTIONAL FISHERY: This is done in gathering oysters in Lake Saroma in under-water method, and gathering immatured scallops. Fishermen depending upon Lake Saroma amount to 320 families. 5. Regional figures of sea products are as follow: one is the large producting district having many kinds of fish and the other is a small producing district having a few kinds of fish. To the former belong Rausu, where maltiple manegement is practised, Abashiri, Mombetsu, Esashi, and Wakkanai, where off-shore fisheries chiefly practised: and to the latter the other regions. 6. The distribution of fishing boats is as follows; (a) region which has a large number of fishingboats, (b) region which has a small number of fishing boats. The former is the region where ships are improved to be large and modernized, and the latter is not. And these agree to each region mentioned in the last section. In short, the fisheries of the coast of the Sea of Okhotsk are, in the eastern parts, coastal fishing based on the base of continental shelf as its fishing place.