Age, Sex and Body Condition of Baltic Grey Seals: Are Problem Seals a Random Sample of the Population?

Kauhala, Kaarina; Kurkilahti, Mika; Ahola, Markus; Herrero, Annika; Karlsson, Olle; Kunnasranta, Mervi; Tiilikainen, Raisa; Vetemaa, Markus

doi:10.5735/086.052.0209

Cited by 15 publications

(12 citation statements)

References 39 publications

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“…Nonetheless, this value could be interpreted as rather low temporal interaction between grey seal foraging activity and local fishing operations. It is important to note that our sample of tracked seals did not contain any adult males, which is a segment of the population believed to have the highest direct interaction with fishing gear in the Baltic Sea 36,65,66 , which contrasts with observations in other regions of the world 67,68 . Future tracking studies should therefore focus on a more balanced sample of individuals across the entire age-spectrum of the population.…”

Section: Discussionmentioning

confidence: 73%

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

Beest

Mews

Elkenkamp

et al. 2019

Sci Rep

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Classifying movement behaviour of marine predators in relation to anthropogenic activity and environmental conditions is important to guide marine conservation. We studied the relationship between grey seal ( Halichoerus grypus ) behaviour and environmental variability in the southwestern Baltic Sea where seal-fishery conflicts are increasing. We used multiple environmental covariates and proximity to active fishing nets within a multivariate hidden Markov model (HMM) to quantify changes in movement behaviour of grey seals while at sea. Dive depth, dive duration, surface duration, horizontal displacement, and turning angle were used to identify travelling, resting and foraging states. The likelihood of seals foraging increased in deeper, colder, more saline waters, which are sites with increased primary productivity and possibly prey densities. Proximity to active fishing net also had a pronounced effect on state occupancy. The probability of seals foraging was highest <5 km from active fishing nets (51%) and decreased as distance to nets increased. However, seals used sites <5 km from active fishing nets only 3% of their time at sea highlighting an important temporal dimension in seal-fishery interactions. By coupling high-resolution oceanographic, fisheries, and grey seal movement data, our study provides a scientific basis for designing management strategies that satisfy ecological and socioeconomic demands on marine ecosystems.

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Section: Discussionmentioning

confidence: 73%

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

Beest

Mews

Elkenkamp

et al. 2019

Sci Rep

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“…In SD30, Königson et al [15] detected specialization of adult grey seal males to salmon catching surface fykes. In addition, based on bycatch statistics of the present data, Kauhala et al [5] classified males from all age groups as potential “problem seals”. Considering all the dietary proxies employed in this work, different commercially exploited fish species, e .…”

Section: Discussionmentioning

confidence: 99%

“…The Baltic grey seal ( Halichoerus grypus ) population has recovered from the low numbers in the 1980s, caused by extensive hunting and environmental toxins, to about 30 000 counted animals [3,4]. Consequently, conflicts with coastal fisheries have increased, mainly due to damage to catch and fishing gear [5] but also because of possible resource competition and bycaught seals [6]. Selective removal of specialized problem seals has been suggested as a method to mitigate damage to fisheries and at the same time avoid overhunting [5,7].…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies have suggested that individual grey seals, instead of being opportunistic, have specialized feeding areas and behaviours [5,15,16]. Although Baltic grey seals are capable of long-distance movements, even between ICES subdivisions, available information suggests that they forage on a more local spatial scale in the vicinity of preferred haul-out areas, however with substantial individual differences [16].…”

Section: Introductionmentioning

confidence: 99%

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Complementary methods assessing short and long-term prey of a marine top predator ‒ Application to the grey seal-fishery conflict in the Baltic Sea

et al. 2019

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The growing grey seal (Halichoerus grypus) population in the Baltic Sea has created conflicts with local fisheries, comparable to similar emerging problems worldwide. Adequate information on the foraging habits is a requirement for responsible management of the seal population. We investigated the applicability of available dietary assessment methods by comparing morphological analysis and DNA metabarcoding of gut contents (short-term diet; n = 129/125 seals, respectively), and tissue chemical markers i.e. fatty acid (FA) profiles of blubber and stable isotopes (SIs) of liver and muscle (mid- or long-term diet; n = 108 seals for the FA and SI markers). The methods provided complementary information. Short-term methods indicated prey species and revealed dietary differences between age groups and areas but for limited time period. In the central Baltic, herring was the main prey, while in the Gulf of Finland percid and cyprinid species together comprised the largest part of the diet. Perch was also an important prey in the western Baltic Proper. The DNA analysis provided firm identification of many prey species, which were neglected or identified only at species group level by morphological analysis. Liver SIs distinguished spatial foraging patterns and identified potentially migrated individuals, whereas blubber FAs distinguished individuals frequently utilizing certain types of prey. Tissue chemical markers of adult males suggested specialized feeding to certain areas and prey, which suggest that these individuals are especially prone to cause economic losses for fisheries. We recommend combined analyses of gut contents and tissue chemical markers as dietary monitoring methodology of aquatic top predators to support an optimal ecosystem-based management.

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“…The possible effects of winter temperature and food quality (herring and sprat weight) on the blubber thickness of male and female pups were tested with correlation and regression analyses. We used only hunted pups because bycaught seals are usually leaner than hunted seals (Bäcklin et al 2011;Kauhala et al 2015). Because most pup data (n = 58) were from the Gulf of Finland, we compared the blubber thickness of pups from the Gulf of Finland in April and May (no data from January-March) with winter temperatures in Russarö and Utö and herring weight in the southern area.…”

Section: Statistical Testsmentioning

confidence: 99%

Delayed effects of prey fish quality and winter temperature during the birth year on adult size and reproductive rate of Baltic grey seals

Kauhala

Kurkilahti

2019

Mamm Res

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Environmental conditions of mammalian juveniles may have delayed effects on their life histories and fitness, such as body size or reproductive rate later in their lives. In the present study, we tested this hypothesis on Baltic grey seals (Halichoerus grypus) and examined (1) the possible effects of prey fish quality and winter temperature on body condition of grey seal pups of both sexes and (2) the possible delayed impacts of pup environment on the body size and birth rate of adult grey seals. Body condition (blubber thickness) of especially female pups in April–May correlated negatively with winter temperatures, and body condition of male pups correlated positively with prey fish quality (herring Clupea harengus and sprat Sprattus sprattus weight). Males reached the asymptotic length at the age of 10.3 years, and body length of adult males (≥ 10 years old) was positively related to herring and sprat weight in their birth year. Females reached the asymptotic length at the age of 5.9 years. Birth rate of females (age 7–24 years) was negatively related to winter temperature in their birth year. We conclude that both changes in prey fish quality and climate may affect body condition of pups and thus also cause delayed effects on adult fitness: body size and reproductive rate of Baltic grey seals.

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Age, Sex and Body Condition of Baltic Grey Seals: Are Problem Seals a Random Sample of the Population?

Cited by 15 publications

References 39 publications

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

Classifying grey seal behaviour in relation to environmental variability and commercial fishing activity - a multivariate hidden Markov model

Complementary methods assessing short and long-term prey of a marine top predator ‒ Application to the grey seal-fishery conflict in the Baltic Sea

Delayed effects of prey fish quality and winter temperature during the birth year on adult size and reproductive rate of Baltic grey seals

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