Bycatch in longline fisheries is considered one of the main threats for the conservation of albatrosses and petrels worldwide. However, the relative impact of fisheries on all the affected populations or species still remains poorly understood. This paper applied a Productivity and Susceptibility Analysis (PSA) and the concept of “Potential Biological Removal Level” (PBR) to assess the relative impact caused by the Uruguayan pelagic longline fishery on several populations. This two-step approach allowed us to obtain an objective view of the relative impact of the Uruguayan pelagic longline fleet on most of the populations or species of albatrosses and petrels with high association with this fishery. Of fifteen species considered, fourteen were finally assessed and a ranking of risk derived. The concept of PBR was applied to the nine most at-risk species. The impact of fishing on populations could not be straightforwardly inferred from their bycatch rates. Results indicate that large albatrosses (Diomedea spp.) and Thalassarche chlororhynchos are more affected than some of the main species caught by the fishery (i.e. Thalassarche melanophrys and Procellaria aequinoctialis). Diomedea exulans from South Georgia is likely to be the population most affected by the Uruguayan fleet. This work should be seen as a case study of the fisheries operating in the southwestern Atlantic. The Uruguayan fleet within its operation area was responsible for only the 4.3% to 12.5% of the total annual effort deployed by the different fleets during 2004–2008. The combined impact of these fleets could be sufficiently high to account for many of the observed declines in the populations of D. exulans, D. dabbenena and T. chlororhynchos. However, the seabird bycatch numbers for most of the pelagic longline fleets that operate in the southwest Atlantic remain unknown. Applying mitigation measures to reduce the impact of pelagic longline fleets operating in this region should be considered a high priority.

This paper is based on recently recovered daily catch and effort data from the Algarve traps (south of Portugal) during the 1898−1900 period. These 18 traps targeted the two migrations of bluefin tuna, entering and leaving the Mediterranean Sea, each year during a period between mid April and the end of August. Their bluefin catches were significant, corresponding to average yearly catches of 61 000 bluefin, i.e., approximately 7900 t. Migration dates and durations towards and away from the Mediterranean Sea were estimated based on the daily catch per unit effort (CPUE) by the traps. Migration patterns were very stable during these three years. The entry migration took place over an average of 42 days, and the return lasted 53 days. Daily catches show large waves of tunas passing during the two migratory phases. It can be hypothesised that each of these waves of tuna spent about 52 days in the Mediterranean Sea, and that each group was stable and consistent during their arrival and return migrations. Migration trajectories along the Algarve coast can be estimated from the daily CPUEs of the different traps. They appear to be different between the arrival and return migrations. The daily data per trap show that most traps caught entering bluefin at quite low CPUE, whereas only a few traps were efficient for catching the returning bluefin, but with much larger catches and CPUEs. The analysis of catch and CPUEs during the entering and leaving phases allowed us to conclude that the catchability and fishing mortality of the bluefin stock in the Algarve trap fishery was much larger during the return migration. Additional daily data from other traps, both historical and contemporary, should be collected and analyzed in order to provide more comprehensive results on the patterns and changes in migration, stock structure and stock exploitation rate.

Hooking (or “at-haulback”) fishing mortality was analysed in elasmobranchs captured by Portuguese longliners targeting swordfish in the Atlantic Ocean. Information was collected by on-board fishery observers who monitored 834 longline fishing sets between August 2008 and December 2011, and recorded information on 36 067 elasmobranch specimens from 21 different taxa. The hooking mortality proportions were species-specific, with some species having relatively high percentages of live specimens at time of haulback (e.g., blue shark, crocodile shark, pelagic stingray, manta, devil and eagle rays), while others had higher percentages of dead specimens (e.g., smooth hammerhead, silky shark, bigeye thresher). For the most captured species (Prionace glauca, Pseudocarcharias kamoharai, Isurus oxyrinchus and Alopias superciliosus), logistic generalized linear models (GLMs) were carried out to compare the mortality rates between sexes, specimen sizes and the regions of operation of the fleet. The sex-specific proportions of hooking mortality were significantly different for blue and crocodile sharks, with the males of both species having higher proportions of hooking mortality than the females. Specimen size was significant for predicting the hooking mortality for blue and shortfin mako sharks: in both cases, the larger specimens had lower odds of dying due to the fishing process. There were differences in the hooking mortality depending on the region of operation of the fleet, but those differences were also species-specific. For blue and crocodile sharks, the hooking mortality was higher in the Equatorial and southern Atlantic areas (when compared to the NE Atlantic region), while the opposite was observed for the shortfin mako, with lower mortality rates in the NE tropical area compared with the other regions. The results presented in this paper can be integrated into future ecological risk assessment analysis for pelagic elasmobranchs. Furthermore, the new information can be used to evaluate the impact of recent recommendations prohibiting the retention of some vulnerable elasmobranch species.

The western Mediterranean is an important fishing area in which the Spanish longline fleet operates. Longline fisheries affect several species of marine mammals, sea turtles, sharks and seabirds, all of which are especially sensitive to fishing mortality. Given international efforts to identify and reduce the bycatch of sensitive species, an onboard observer program was implemented by the Spanish Oceanographic Institute (IEO, Instituto Español de Oceanografía). The aim of the present study was to report data on marine mammal bycatch in the western Mediterranean. The additional aim was to improve knowledge about the possible effects of the Spanish longline fisheries on cetacean populations, particularly Risso’s dolphin, and to suggest improvements to fisheries management. Data on marine mammal bycatch were collected during the period 2000–2009. Differences are reported for catch per unit effort (CPUE, defined as marine mammals per 1000 hooks) for each type of gear (n = 7), as well as their effect on specific marine mammal species. A total of 5 398 297 hooks were monitored, which yielded 56 marine mammals belonging to 4 different species. Our results indicate that Risso’s dolphin is the species most affected by the longline fishery in the western Mediterranean (n = 33). We built a predictive model for Risso’s dolphin bycatch using variables associated with the technical characteristics of the fishery, geographic location and seasonality. We performed a binary logistic regression of the presence/absence of Risso’s dolphin bycatch to test whether the probability of incidentally catching one or more dolphins may be predicted by some of the explanatory variables selected. Our results indicate that Risso’s dolphin was mainly caught using Japanese longline (LLJAP) or an experimental home-based longline (LLHBexp) over the continental shelf. Because LLHBexp is an experimental type of gear that was only used occasionally by the fleet, controlling the use of LLJAP over the continental shelf could strongly reduce the impact of these fisheries on populations of Risso’s dolphin in the western Mediterranean.

Virtual population analysis requires information on the fishing mortality rate (or abundance) for one age group from each cohort. In many cases available data are insufficient to estimate these rates for every age group and structural assumptions must be imposed to reduce the number of effective parameters. Past assessments of western Atlantic bluefin tuna (Thunnus thynnus) have reduced the number of parameters by assuming pre-specified values for the ratios of the fishing mortality rates on adjacent age groups. More recent bluefin tuna assessments have estimated terminal fishing mortality rates (F) on each age with a constraint that restricts change from one year to the next. We explore the implications of these methods of estimating terminal-year F through retrospective analyses of the 2006 bluefin tuna assessment and through stochastic simulations. The use of pre-specified ratios for F created strong retrospective biases and may have led to overly optimistic projections. Constraining annual changes in the terminal-year F appeared to mute retrospective patterns and resulted in abundance projections less prone to spurious initial leaps. Simulation results indicate that the constraint improves estimation, particularly with moderate to low interannual changes in selectivity.

The Chilean jack mackerel (Trachurus murphyi) is one of the most important exploited fish populations in the world. Its area of distribution covers the sub-tropical waters of the South Pacific Ocean, from South America up to New Zealand and even Australia. It is subject to high variations in biomass, with annual world catches varying from less than 0.5 to almost 5 million tonnes. Management of this species and its fishery requires a correct understanding of the population structure. Although several hypotheses have been proposed, suggesting that there are up to four independent populations, genetic analysis indicates only a single population in the South Pacific Ocean. We consider the two most probable structures for this population: a “patchy population”, where all the fish belong to a single population that expands and contracts depending on the biomass; and a metapopulation, where a source population creates several subpopulations that can remain independent during prolonged periods, depending on the environmental conditions. We studied the conditions for these hypotheses to represent reality, especially the demographic structure and existence of different spawning areas. Using knowledge obtained from fisheries and acoustic surveys, we show that if we apply their definitions strictly, neither of the two hypotheses can be fully rejected. Nevertheless, some particular spatial characteristics observed recently between the Peruvian and Centre-South Chilean parts of the distribution lead us to conclude that the metapopulation definition is likely to better describe the stock. The consequences of each population structure for fisheries management are listed, showing that the metapopulation hypothesis represents a safer definition for stock assessment. We conclude that T. murphyi can be described as a metapopulation, but also that the definitions proposed in the literature on metapopulations are not fully adapted to pelagic fish populations with a basin-scale distribution range, and suggests specific research that could be done in this field.