Search The Database

Information on seal bycatch in Irish fisheries were collected through an onboard observer program. The gillnet fishery had no observed bycatch of seals. Grey seals (Halichoerus grypus) and harbor seals (Phoca vitulina) were caught as bycatch in large mesh tangle nets targeting crawfish (Palinurus elephas). The west and southwest coasts of Ireland have a high risk for seal bycatch in crawfish fisheries due to the presence of grey seal colonies and similar habitat preferences. There was a positive correlation between seal bycatch and crawfish and monkfish catches, depth of gear deployment and large mesh sizes. Improved net visibility, smaller mesh sizes and the use of pots instead of tangle nets may help reduce these bycatch interactions. 

This study used systemic scar analysis to estimate the frequency of non-lethal entanglements among humpback whales (Megaptera novaeangliae) off the coast of Iceland from 2005-2017. Results demonstrate that at least 24.8% of individuals had prior entanglement(s) when first encountered, and then subsequently acquired new entanglement-related injuries at an average rate of 1.9% per year; however, scar-based estimates usually underestimate the frequency of prior entanglements. At least some entanglements seem to have occurred locally. 

This paper focuses on mitigation measures specified by the International Commission for the Conservation of Atlantic Tunas (ICCAT) related to threatened seabirds foraging in the south Atlantic Ocean. The authors developed an ecological risk assessment for various combinations of mitigation measures to protect five threatened albatross and petrel populations, comparing those specified by ICCAT to those recommend by the Seabird Bycatch Working Group of the Agreement on the Conservation of Albatrosses and Petrels (ACAP). They conclude that updating existing mitigation measure specifications for pelagic longlining in the South Atlantic to reflect current best practice guidelines would potentially reduce seabird mortality by 41–86 %, and predict that simultaneous application of all three ACAP recommended mitigation measures recommended (includingnight setting, branch line weighting, bird-scaring lines, and hook shielding devices) could reduce seabird mortality by 72–93 % and therefore should be considered by ICCAT.

This study analyzed seabird bycatch data across gear types in the Greenland halibut (Reinhardtius hippoglossoides) fishery spanning 2019-2019. Northern fulmars (Fulmarus glacialis) were the most frequently reported seabird bycatch species, with August, September and October having the highest levels caught. Seabird bycatch overall was highly variable between years, but did not seem to be related to the level of total allowable catch.

A meta-analysis of 15 papers examined the general impact of seabird bycatch reduction device (BRD) technology on commercial longline fishing operations. Since there were relatively few papers with data suitable for meta-analysis, the researchers pooled studies with BRD-and fishery-related metrics included as covariates. The analysis found a small (9%) increase in target catch with BRD use in longline fisheries, while seabird bycatch was reduced by 89%. This pattern does not change with respect to geographic location or BRD type, indicating that efforts to reduce seabird bycatch are generally effective under different conditions. 

Cory's shearwater, Calonectris diomedea, is the main seabird species incidentally caught by the Spanish longline fleet in the western Mediterranean Sea. The authors used onboard observer data to model the longline bycatch of Cory's shearwaters as a function of time of the year, technical characteristics of the fishing operation, and geographical location. The most explanatory factor for bycatch was the geographical location and then the technical characteristics (number of hooks and fishing during non-working days). Seabirds are more likely to approach longline vessels when trawlers are not allowed to operate (non-working days), so the authors conclude that activity of longliners should be limited to working days.  

This study summarized trends in United States marine mammal bycatch from 1990-2017. Total annual bycatch was estimated to be 4296 ± 1789 individuals, and the vast majority occurred in gillnets; 52% of marine mammal bycatch consisted of pinnipeds, while the other 48% was cetaceans. Total marine mammal bycatch in U.S. fisheries declined from 1990 to 2002 following the passage of the Marine Mammal Protection Act in 1972, but there was no change in total bycatch from 2002 to 2017, suggesting that U.S. bycatch mitigation measures has had some success. While bycatch levels declined through 2017 in the Atlantic-Gulf of Mexico-Caribbean region, reductions either halted or increased in the Pacific and Atlantic regions by 2006. 

This study attempted to hydrodynamically optimize Turtle Excluder Devices (TEDs) in trawl fishing nets in order to balance bycatch reduction with operational efficiency. Researchers conducted flume test experiments on different TED configurations (bar spacing, installation angle, and flow velocity) in a model shrimp trawl, and used Fast Fourier Transform analysis (FFT) to understand the hydrodynamic force oscillations. The presence of a rigid TED increases mean codend drag by 26.2% to 42.1% compared to an empty codend, with drag amplifying as bar spacing decreases and as installation angle and flow velocity increase. A Genetic Algorithm framework identified the optimal TED configuration as an 88 mm bar spacing, a 60° installation angle, and a 0.6 m/s flow velocity. This optimized configuration achieved substantial improvements, reducing mean drag by 45.25%, suppressing drag oscillation amplitude by 64.87%, and improving relative codend stability by 28.76%. 

Researchers used data from long-term cetacean and fisheries monitoring programs in the Santos Basin of Brazil to assess the spatial overlap between cetaceans and gillnet fisheries, identify areas of high potential bycatch exposure, and determine the relative susceptibility of cetacean species to these interactions. Gillnet fisheries concentrate primarily along the continental shelf, overlapping the most with Guiana dolphin (Sotalia guianensis), Franciscana (Pontoporia blainvillei), and bottlenose dolphin (Tursiops truncatus). The Guiana dolphin and the Franciscana appear particularly vulnerable due to their conservation status and habitat use. Researchers also identified priority areas for bycatch risk assessment and management, including a region of high cetacean diversity. 

This study examines the occurrence of cumulative cold events in the Gulf of Ulloa, Baja California (Mexico), defined as sea surface temperatures (SST < 18°C) for ≥5 consecutive days, as a basis for developing an operational environmental indicator to support adaptive fisheries management and reduce sea turtle bycatch. Results indicate a clear seasonal pattern, with the highest frequency of cold events between March and June, coinciding with intensified coastal upwelling and the residence of juvenile Caretta caretta. Eighteen critical areas of persistent environmental conditions were identified as overlapping with areas of turtle-fishery interactions. This indicator could provide near-real-time environmental information to anticipate sea turtle vulnerability and support conservation decisions without relying on static fishery closures.