Managing Marine Mammals and Fisheries: A Calibrated Programming Model for the Seal-Fishery Interaction in Sweden

This paper develops a model based on the concept of Positive Mathematical Programming (PMP) that is useful for ex-ante analyses of how policy measures affect commercial fisheries. PMP models are frequently used in agriculture, but rarely for analyzing fisheries. Fisheries often face a large set of constraints such as effort regulations and catch quotas of which some might be binding and others not. An econometric approach is developed for calibrating models with both binding and non-binding constraints. The interaction between seals and Swedish fisheries is used as an empirical application. Seal interaction is modeled as seals predating fish from passive gear (nets and hooks), which is primarily an issue for the coastal fishery. The model contains 24 fleet segments involved in 247 different fishing activities in 2012. The results show that if no further management action is taken, fisheries using passive gear will reduce their activities from about 46 000 days at sea per year to about 41 000 and reducing their economic performance from losses of about 2 million Euros to about 3.3 million. The impact from seals can be reduced by reducing the seal population or providing economic compensation.

Summer coastal rookeries and perspectives of the Baikal seal (Pusa sibirica) population in the conditions of the global warming

Based on the secondary literature, a retrospective characterization of the climate in the Baikal region, starting from the end of the Pleistocene, is given. According to satellite monitoring data, the characteristics of the ice regime of the Lake Baikal in the conditions of climate warming are presented. Moreover, we briefly discuss the impact of climate change on the ecology and biology of the Baikal seal (Pusa sibirica Gm.). Using video materials obtained online at one of the main island coastal rookeries of seals (on the island of Tonkyi, the archipelago of the Ushkany Islands, Lake Baikal) in 2011–2017, the dependence of the number of seals hauled out on the lake level and the peculiarities of the fishing regime was determined (the survey was conducted from May–June to October). A direct relationship was determined between the relative number of animals that had a moulting delay and the ice regime of a given year: the longer the floating ice in the northern part of Lake Baikal remained, the more numerous were the first approaches of seals to the studied rookery and the greater was the proportion of moulting individuals. It is reasonable to assume that the main reason for the Baikal seal to come ashore is not prolongued moulting time, but a physiological need for sunlight, which has a healing effect on the body of animals that lack solar radiation in winter. In general, climate warming has a negative impact on the state of the Baikal seal population. The available paleoclimatic reconstructions of the Holocene indicate that the population of the Baikal seal has experienced a lot of climate changes in its history. Nevertheless, if the current trends of climatic changes persist until the end of the 21st century, the ecology and biology of the seal will drastically change (up to the beginning of terrestrial reproduction), and the population will significantly decrease. However, the Baikal seal as a species would remain.

First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population.

The status of the fur seal population (Arctocephalus gazelle) on the southern border of the distribution area (the Argentine Islands archipelago)

The study of the population status of Arctocephalus gazella (Peters, 1875) in waters of the Argentine Islands was carried out in the period from April 2015 to March 2016 in accordance with the objectives of the State Target Scientific and Technical Research Program of Ukraine in Antarctica for 2011–2020. The aim of the article is to study the population dynamics and distribution of the southern fur seal in waters of the Argentine Islands. Due to the lack of data on the specifics of the seal’s dispersal in different periods of the year and the dynamics of the species population at the southern border of the distribution range, the results of the research are relevant and of great importance. In the second half of the 20th century, some publications presented the results of monitoring of pinnipeds at the Argentine Islands and adjacent territories, but the objects of these studies usually were other seal species: Hydrurga leptonyx, Lobodon carcinophagus, Leptonychotes weddelli, and Mirounga leonina. In the early 21st century, monitoring of the fauna of the Argentine Islands was carried out by Ukrainian biologists. However, they focused on Leptonychotes weddelli and less on other species of pinnipeds. The field material was collected in waters of the Argentine Islands, which is located in the Pacific sector of Antarctica. The fur seal population census and distribution studies were conducted according to the generally accepted methods. After breeding season on the subantarctic islands, during the migration southwards, fur seals reach the Argentine Islands, usually in the third decade of January. In the summer of 2016, the first fur seal was recorded within the archipelago on 31 January. During the study period, the largest number of animals within the archipelago was recorded in March–April and it ranged from 300 to 400 individuals. On the islands of the archipelago, the main resting places of seals were identified. The movement of animals northwards starts in May, consequently a decrease in the number of animals in this region is observed at that time. The last individuals are recorded in the first half of August. In 2015, migration began in May and ended in early August. There are several periods that were characterized by intensive migration of the animals: late June, 5–8 July, and 29 July to 6 August. In winter, one individual was last found within the archipelago on 12 August. The migration is launched by the worsening of weather conditions, formation of a continuous ice cover, reduced availability of food, and other factors.

The Role of Food Web Interactions in Multispecies Fisheries Management: Bio-economic Analysis of Salmon, Herring and Grey Seal in the Northern Baltic Sea

Multispecies bio-economic models are useful tools to give insights into ecosystem thinking and ecosystem-based management. This paper developed an age-structured multispecies bio-economic model that includes the food web relations of the grey seal, salmon, and herring, along with salmon and herring fisheries in the Baltic Sea. The results show that the increasing seal population influences salmon fisheries and stock, but the impacts on the harvest are stronger than on the stock if the targeted management policies are obeyed. If seal population growth and a low herring stock occur simultaneously, the salmon harvest could face a serious threat. In addition, scenarios of the multispecies management approach in this paper reveal a benefit that our model can evaluate the performance of different fisheries with identical or different management strategies simultaneously. The results show the most profitable scenario is that both fisheries pursuit aggregated profits and reveal a trade-off between herring fisheries and salmon fisheries. Our model indicates that the herring harvest level and the approaches to managing herring fisheries can influence the performance of salmon fisheries. The study also demonstrates a way to develop a multispecies bio-economic model that includes both migratory fish and mammalian predators.

The relative effectiveness of two expanding bullet designs in young harp seals (Pagophilus groenlandicus): A randomised controlled field study in the Norwegian harp seal hunt

The aim of this study was to investigate the relative effectiveness of a rapidly expanding Bonded hunting bullet and an explosively expanding Varmint bullet in young harp seals (P). The study was conducted as an open, controlled and randomised parallel-group designed field trial. The animals were pre-randomised (1:1) into one explosively expanding (Varmint) and one expanding (Bonded) bullet type group, with 75 animals in each. The study sample consisted of young, weaned harp seals, 2–7 weeks of age, of both sexes, from the Greenland Sea harp seal population. The study was conducted during the regular hunt. Instantaneous death rate (IDR) and time to death (TTD) were the main variables. The observed IDR was 84 in both bullet groups. Correcting for Weather Condition Index, the IDR for the Varmint bullet was significantly higher compared to the Bonded. The mean TTD was shortest in the Varmint group, but the difference did not reach significance. Compared to the Bonded, a significantly higher total cranial damage score and bleeding intensity, and significantly lower frequencies of bullet exit wounds were detected in the Varmint group. The post mortem reflex movements caused by the Varmint bullet were significantly more powerful with longer duration and higher frequencies of clonic contractions. In conclusion, the results indicate a higher effectiveness of the Varmint bullet relative to the Bonded. The Varmint bullet may thus improve animal welfare in the hunt of young harp seals.

Enhanced chlorophyll-a concentration in the wake of Sable Island, eastern Canada, revealed by two decades of satellite observations: a response to grey seal population dynamics?

Elevated surface chlorophyll-a concentration, an index of phytoplankton biomass, has been previously observed and documented by remote sensing in the waters to the southwest of Sable Island (SI) on the Scotian Shelf in eastern Canada. Here, we present a detailed analysis of this phenomenon using a 20-year time series of satellite-derived chlorophyll-a concentration (chl-a), paired with information on the particle backscattering coefficient at 443 nm (bbp(443)) and the detritus/gelbstoff absorption coefficient at 443 nm (adg(443) ) in an attempt to explain the possible mechanisms that lead to the increase in surface biomass in the surroundings of SI. We compared the seasonal cycle, climatology and trends of surface waters near SI to two control regions located both upstream and downstream of the island, away from terrigenous inputs. Application of the self-organizing maps approach (SOMs) to the time series of satellite-derived chl-a over the Scotian Shelf revealed the annual spatio-temporal patterns around SI and, in particular, persistently high phytoplankton biomass during winter and spring in the leeward side of SI, a phenomenon that is not observed in the control boxes. Time series analysis of the satellite archive evidenced a long-term increase in chl-a and adg(443), and a long-term decrease in bbp(443) in all regions. In the close vicinity of SI, the increase of chl-a and adg(443) during the winter months occurred at a rate twice that of the ones observed in the control boxes. In addition to the increase of the chl-a and adg(443) within the plume southward of SI, the surface area of the plume itself has also expanded by a factor of five over the last 20 years. While the island mass effect (IME) is certainly contributing to the enhanced biomass around SI, we hypothesize that the large increase in chl-a over the last 20 years is due to an injection of nutrients by the island’s grey seal colony, which has increased by about 300 % over the last twenty years. The contribution of nutrients from seals may sustain high phytoplankton biomass at a time of year when it is usually low. A conceptual model was developed to describe the annual variation of seal abundance on SI and estimate the standing stock of chl-a concentration that can be sustained by the release of nitrogen. Comparison between satellite observations and model simulations showed a very good agreement between the seal population increase on SI during the breeding season and the phytoplankton biomass increase during the winter. In addition, the 20-year satellite-derived trend in chlorophyll-a concentration showed a good agreement with the increasing trend in seal population on SI during the same time period. The satellite data analysis supports the concept of top-down control of marine mammals over lower trophic levels through a fertilisation mechanism, although these results could not be confirmed without in situ measurements for ground truthing. Our findings challenge the idea that the IME is restricted to islands with strong bathymetric slope located in oligotrophic waters of mid-latitudes and tropics, and demonstrate that enhanced marine production can occur in other oceanic regions, with potentially substantial implications for conservation and fisheries.

Demography and population structure of Northeastern mediterranean monk seal population

The Northeastern Mediterranean coasts that border southern Turkey host one of the last strongholds for the survival of the endangered Mediterranean monk seal (Monachus monachus, 1779). The seal colonies inhabiting south coast of Turkey have been studied since 1994 through various short-term research projects focusing on distinct small populations that were thought to be isolated. In this study, the entire extent of the area was monitored approximately for 3 years (between 2015 and 2018) with camera traps places in 20 caves known to be actively used by the seals. A total of 7014 images taken throughout the study period, along with 25,100 images taken previously, were used to identify the seals inhabiting the area. In total, 37 individuals were identified based on the natural marks on the body. Based on photo-identified seals, a mark-recapture method was applied to estimate the total population size within the Northeastern Mediterranean. The overall population size was found to be 46 (SE=7.7) in the case of closed population and 53(SE=34.8) in the case of open population during the study period. The range of identified seals was almost six times larger than previously documented in the same area, reaching distances up to 245 km. The population estimate indicated a decrease in population size compared to previous studies. Finally, the study emphasises the importance of long-term monitoring studies elucidating changes in the demographic parameters in relation to threats posed, rather than cut-paste measurement suggestions which are not applicable in reality, while structuring the conservation actions targeting survival of this highly endangered species.