Tuna and swordfish catch in the U.S. northwest Atlantic longline fishery in relation to mesoscale eddies

To analyze the effects of mesoscale eddies, sea surface temperature (SST), and gear configuration on the catch of Atlantic bluefin (Thunnus thynnus), yellowfin (Thunnus albacares), and bigeye tuna (Thunnus obesus) and swordfish (Xiphias gladius) in the U.S. northwest Atlantic longline fishery, we constructed multivariate statistical models relating these variables to the catch of the four species in 62 121 longline hauls made between 1993 and 2005. During the same 13‐year period, 103 anticyclonic eddies and 269 cyclonic eddies were detected by our algorithm in the region 30–55°N, 30–80°W. Our results show that tuna and swordfish catches were associated with different eddy structures. Bluefin tuna catch was highest in anticyclonic eddies whereas yellowfin and bigeye tuna catches were highest in cyclonic eddies. Swordfish catch was found preferentially in regions outside of eddies. Our study confirms that the common practice of targeting tuna with day sets and swordfish with night sets is effective. In addition, bluefin tuna and swordfish catches responded to most of the variables we tested in the opposite directions. Bluefin tuna catch was negatively correlated with longitude and the number of light sticks used whereas swordfish catch was positively correlated with these two variables. We argue that overfishing of bluefin tuna can be alleviated and that swordfish can be targeted more efficiently by avoiding fishing in anticyclonic eddies and in near‐shore waters and using more light sticks and fishing at night in our study area, although further studies are needed to propose a solid oceanography‐based management plan for catch selection.     

Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with potentially large consequences

1. The purpose of this study was to investigate the effects of a circle hook ring on catch rates of target fish species and bycatch rates of sea turtles, elasmobranchs, and non‐commercial fish in a shallow‐set Italian swordfish longline fishery.
2. Results were compared from 65 sets from six commercial fishing vessels totalling 50 800 hooks in which ringed and non‐ringed 16/0 circle hooks with a 10° offset were alternated along the length of the longline. In total, 464 individuals were caught in the 4 years of experiment, with swordfish (Xiphias gladius) comprising 83% of the total number of animals captured. Catch rates of targeted swordfish were significantly higher on ringed hooks (CPUE_{ringed hooks} = 8.465, CPUE_{non‐ringed hooks} = 6.654).
3. Results indicate that ringed circle hooks captured significantly more small‐sized swordfish than non‐ringed circle hooks (27.7% vs. 19.5%, respectively).
4. For species with sufficient sample sizes, the odds ratio (OR) of a capture was in favour of ringed hooks; significantly for swordfish (OR = 1.27 95%CI 1.04–1.57), and not significantly for bluefin tuna (Thunnus thynnus) (OR = 1.50, 95%CI 0.68–3.42) nor for pelagic stingray (Pteroplatytrigon violacea) (OR = 1.13, 95%CI 0.54–2.36). All six loggerhead turtles (Caretta caretta) and three of the four blue sharks (Prionace glauca) were captured on ringed hooks, however, the small sample sizes prevented meaningful statistical analysis.
5. In summary, results from this study suggest that the addition of a ring to 16/0 circle hooks confers higher catchability for small‐sized commercial swordfish, and does not significantly reduce catch rate of bycatch species and protected species in a Mediterranean shallow pelagic longline fishery.
6. These findings should motivate fisheries managers to consider factors in addition to hook shape when aiming to promote sustainable fishing practices. The presence of a ring has the potential to negate some conservation benefits.

Copyright © 2016 John Wiley & Sons, Ltd.     

西南大西洋阿根廷滑柔鱼渔业中国大陆鱿钓船CPUE标准化

阿根廷滑柔鱼是我国重要的头足类渔业之一，对其单位捕捞努力量渔获量( CPUE)进行标准化是对其资源评估的重要内容。本研究根据2000～2010年我国在西南大西洋的产量统计数据和卫星遥感获得的海洋环境数据（表温，表温水平梯度，海面高度，叶绿素浓度），利用广义线性模型（GLM，general linear model）和广义加性模型（GAM，generalized additive model）对其CPUE进行标准化。GLM模型结果表明，年、纬度、表温以及交互项年与纬度对CPUE影响最大。GAM模型研究结果表明，年、月、经度、纬度、表温、海面高度以及交互项年与纬度、年与经度对CPUE影响较大。根据AIC数值，包含上述8个显著变量的GAM模型为最佳模型，对CPUE的解释率为49.20%。高CPUE出现在夏季表温为12～16°C、海面高为-20~20cm、46.5°～48.5°S海域。研究表明，GAM模型较GLM模型更适合用于西南大西洋阿根廷滑柔鱼CPUE标准化。     

Are circle hooks effective management measures in the pelagic longline fishery for sharks in the Gulf of Gabès?

1. This study evaluated the circle hook use as a tool for shark management in the pelagic longline fishery in the Gulf of Gabès.
2. The usual J‐hook No. 2 with 10° offset, which has been traditionally used by the fishery, was compared to the 18/0 non‐offset circle hook in an alternating fashion along the main line. In total, 22 experimental longline sets were deployed through the shark fishing seasons of 2016 and 2017 to examine the effects of hook types on the catch composition, the catch rates, the hooking location, and the status at haulback.
3. The catch composition differed significantly among hook types. Moreover, an overall increase in catch rates for the main species, the sandbar shark Carcharhinus plumbeus, and the shortfin mako shark Isurus oxyrinchus, was observed when using circle hooks.
4. There was no size‐selective effect of circle hooks for the common species. The circle hooks were not effective at reducing at‐haulback mortality of sandbar shark. Conversely, shortfin mako and smooth‐hound shark Mustelus mustelus showed significantly lower relative mortality at haulback with circle hooks than with J‐hooks. Furthermore, circle hooks were more frequently hooked externally than the J‐hooks for the three shark species.
5. Results demonstrated that the use of 18/0 non‐offset circle hooks in the pelagic shark longline fishery can reduce mortality at haulback for some species without any benefit for the dominant species, the sandbar shark.
6. Overall, it is difficult to promote the adoption of the use of circle hooks as a management measure in this specialized fishery. Management measures focusing on fishing effort controls, fishing closures in critical habitats, and size limits could have significant benefits for the conservation of shark species and may help to improve the sustainability of the shark fishery in the Gulf of Gabès.

     

Accuracy and precision of archival tag data: a multiple-tagging study conducted on a whale shark (Rhincodon typus) in the Indian Ocean

Pop‐up satellite archival tags (PSATs) are now widely used to document the geographic and vertical movements of large pelagic fishes. These instruments record measurements of ambient light, depth and temperature at regular intervals and the light data are used to compute daily estimates of latitude and longitude. Several methods have been developed to improve those estimates, including the application of Kalman filter models and matching sea surface temperatures (SST) from tags with remotely sensed SSTs. Despite their widespread use, few studies have evaluated the accuracy of raw estimates of location from PSATs or quantified the improvements that may result from refinement techniques. To assess the accuracy of raw and refined estimates of locations from PSATs, we attached two PSATs and one Argos satellite‐linked transmitter (SAT tag) to one whale shark (Rhincodon typus) at Ningaloo Reef, Western Australia. The root mean square error (RMSE) in raw estimates of location provided by the PSATs was 5.16° latitude and 2.00° longitude. Estimates were more accurate after processing the data with a Kalman filter (RMSE = 2.97° latitude and 0.78° longitude) and most accurate after processing with a Kalman filter model that integrates SST measurements (RMSE = 1.84° latitude and 0.78° longitude). We also assessed the precision of the PSAT‐derived locations, and depth and temperature measurements by comparing the data from the two PSATs. Our findings support the use of archival tag data to reconstruct the large‐scale movements of marine animals and demonstrate the significant improvements that may result from two refinement techniques.     

Characterizing larval swordfish habitat in the western tropical North Atlantic

Swordfish Xiphias gladius (Linnaeus, 1758) are a circumglobal pelagic fish targeted by multiple lucrative fisheries. Determining the distribution of swordfish larvae is important for indicating reproductive activity and understanding the early life history of swordfish. We identify and characterize larval swordfish distributions during peak swordfish spawning throughout the Gulf of Mexico and western Caribbean Sea with generalized additive models (GAMs) using catches of swordfish larvae during ichthyoplankton surveys in April and May of 2010, 2011, and 2012. The best fit GAM, as determined by stepwise, backward Akaike Information Criterion selection, included both physiochemical (temperature at 5 m, sea surface height anomaly (SSHA), eddy kinetic energy (EKE)), temporal (lunar illumination, hour of sampling) and spatial (location) variables, while near surface chlorophyll a concentration residuals remained as a random effect. The highest probability of larval swordfish catch occurred at sub‐surface temperatures, SSHA, and EKE values indicative of boundary currents. Standard lengths of larvae were larger further downstream in the boundary currents, despite high variability in length with location due to multiple spawning locations of swordfish near these currents. Probability of larval swordfish catch also peaked during the crescent and gibbous moons, indicating a lunar periodicity to swordfish spawning. These results suggest that swordfish may spawn during select moon phases near boundary currents that transport their larvae to larval and juvenile habitat including the northern Gulf of Mexico and coastal waters of the southeast United States.     

热带大西洋金枪鱼延绳钓兼捕鲨鱼种类组成和渔获率及其与表温的关系

根据2007年12月~2008年3月采集的热带大西洋(05°37′~12°01′N、29°00′~36°51′W)金枪鱼延绳钓渔获物数据,分析了金枪鱼延绳钓兼捕鲨鱼的种类组成、渔获量、渔获率及其与表温的关系。本次调查共捕获鲨鱼8种,隶属3目7科7属,总渔获尾数为633 ind,总渔获量达26 837.4 kg,其中大青鲨为主要兼捕种类。各种鲨鱼渔获率平均值在0.003~1.524 ind/1 000 hooks之间,其中大青鲨最高,其值为1.524 ind/1 000 hooks,大眼砂锥齿鲨最低,其值为0.003 ind/1 000 hooks。各种鲨鱼渔获率月变化不明显(ANOVA,P=0.901)。鲨鱼总渔获率和大青鲨渔获率与表温都呈显著性负相关。大青鲨主要出现渔场的表温范围为24.6~25.8℃。     

热带大西洋西部水域大眼金枪鱼延绳钓渔场分布及其与表温之间的关系

根据2004年9月至2005年3月农业部渔业观察员项目在热带大西洋西部水域调查所获得的渔业数据和现场表温数据,结合哥伦比亚大学网站下载的1°×1°表温资料,利用地理信息系统(GIS)软件Marineexplore 4.0图示了各月钓获率及钓获率与表温关系的分布并进行分析。结果表明,2004年11月的产量和CPUE均达到最高,分别为24.539 t和0.332 t/v.d。调查期间,各月钓获率大部分(80.3%)分布在表温高于26.0℃。     

Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

1. This paper reports the results of using different hook style and bait type combinations on the catches of targeted, bycatch and discarded fishes in the Portuguese commercial longline fishery targeting swordfish (Xiphias gladius) in the South Atlantic Ocean.
2. In total, 310 longline experimental sets (446 400 hooks) were deployed between October 2008 and February 2012. Three different hook styles were tested; the traditional J‐hook (9/0) 10^o offset was compared with two 17/0 circle hooks (a non‐offset and a 10^o offset), and squid (Illex spp.) bait was compared with mackerel (Scomber spp.).
3. Catch per unit effort (CPUE) was calculated for each fish species per fishing set and compared between the different hook style and bait type combinations. Results indicated that the effects of hook style and bait on the CPUEs were species‐specific. For example, swordfish (target species, Xiphias gladius) CPUEs were higher with J‐hooks baited with squid, while for the blue shark (most important bycatch species, Prionace glauca) the highest CPUEs were obtained with circle hooks baited with mackerel. For tuna (Thunnus spp.) and marlin (blue, Makaira nigricans and white, Kajikia albida) only the bait effect was significant, with higher catches with squid.
4. For the discarded species, the proportions of alive vs dead specimens at the time of fishing gear retrieval were also species‐specific.
5. The total retained catch value per unit of effort (VPUE) did not changed between the different hook and bait combinations, but these VPUEs are highly dependent on market fluctuations.

Copyright © 2014 John Wiley & Sons, Ltd.     

Climate and stock influences on the spread and locations of catches in the northeast Atlantic mackerel fishery

The poleward movements of northeast Atlantic (NEA) mackerel (Scomber scombrus) catches, possibly linked to climate change, are causing a major international disagreement over quotas. We present an analysis of spatially resolved catch data from 1977 to 2013 that shows how a northward shift is only part of the change in the fishery. There was a 30‐yr trend for declining catches per ICES rectangle (0.5° latitude by 1°‐degree longitude) until 2011–2013. Catches also moved further offshore, to areas of deeper waters. Segmented regressions suggested discontinuities in the temporal pattern of change in catch‐related variables. In particular, the number of ICES rectangles fished rose sharply around 1987. Generalized additive models (GAMs) suggest that much of the movement of fishing activity to areas of deeper water can be associated with variation in the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). GAM models had a lower predictive error than linear or simple autoregressive models of change in catch‐related variables. Although climate indices can be linked to some of the changes in catch, it may be difficult to extrapolate future patterns in the catch: some of the GAM smoothers are non‐linear, and the oceanographic processes linked to climate index values are not homogenous across the area occupied by mackerel. A practical implication of the reported changes in catch since 1977 is that vessels are now reportedly fishing further offshore, which has implications for fuel consumption and profitability of the fishery.