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Here we introduce a new integrated population model (IPM) to provide harvest advice for the Gulf of St. Lawrence (Gulf), Coastal Nova Scotia (CNS) and Sable Island grey seal herds, and compare model outputs with estimates from a deterministic model used in previous assessments. The IPM was fit to the pup production estimates for the Scotian Shelf (CNS and Sable Island combined) and the Gulf. As with the previous assessment model, the new model was fit to both pup production and pregnancy rates, and includes an index for ice-related pup mortality in the Gulf. The new model includes both density-dependent and density-independent pup mortality, and fits to sighting histories of individually marked seals at the breeding colony on Sable Island to estimate sex- and age-specific survival and recruitment to the breeding colony. The model estimated that total pup production increased slightly from 92,300 (95% CI = 86,700-100,100) in 2016 to 99,300 (90,900-107,700) in 2021, while total abundance increased slightly from 339,400 (317,900-361,500) in 2016 to 366,400 (317,800-409,400) in 2021. The rate of growth of the population has continued to slow, declining from approximately 4% during the last assessment period, to 1.5% per year between 2016 and 2021. The updated population estimate from the previously accepted deterministic population model was 363,600 (298,700-450,000) for 2021, which is very similar to the estimate of abundance generated using the IPM. Although the population continues to grow, the current estimate is below that presented during the 2016 assessment. The difference is due to changes in the structure of the new population model and higher estimates of juvenile mortality produced by the model fit to the 2021 pup production estimates. Additional information on juvenile survival and how it responds to changes in abundance (density-dependent) and environmental (density independent) variation is needed as it represents a significant gap to our understanding of the dynamics of this population and of large marine mammals in general. Total allowable removals depend on age structure of the harvest and whether the harvests are conducted in winter at the breeding colonies, or at other times of the year when animals from all herds are mixed. Using an integrated model incorporates many of the inputs in a unified framework that allows for uncertainty to be propagated throughout the analyses. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Science Advisory Secretariat Research Document is the property of Her Majesty the Queen in Right of Canada as represented by the Minister of Fisheries & Oceans and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Science Advisory Secretariat Research Document is the property of Her Majesty the Queen in Right of Canada as represented by the Minister of Fisheries & Oceans and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

After more than four decades of growth at 13%, the rate of pup production of Grey Seals (Halichoerus grypus) at Sable Island has declined to about 4% per year. As resource limitation becomes more acute, life history theory suggests that first juvenile survival, then adult fertility, and finally adult survival will change. Previously, mark-resight analysis of Grey Seals on Sable Island found that juvenile survival had been reduced by almost 50% between the early 1990s and early 2000s, suggesting that resources may have become limiting for this population. Here, we fit a Cormack-Jolly-Seber model to the resighting history of individually marked Grey Seals that have recruited to the Sable Island breeding colony since 1978 to estimate age- and sexspecific adult survival. Of those initially marked, 562 males and 1728 females were resighted in the breeding colony between 1978 and 2016. Average adult survival was high (male=0.943, Standard Error (SE)=0.003; female=0.976, SE=0.001), but male Grey Seals had lower survival at all ages. Resighting probability has remained between 60 and 80% since the late 1980s. Males are more likely to be sighted in a breeding season than females. Only female Grey Seals with pups are regularly sighted on the breeding colony; thus, those females that skip breeding are unobservable (temporary emigration). A multi-state open robust design model was used to estimate the transition probabilities between breeding (observable) and non-breeding (unobservable) states for individually marked females that were observed on the colony from 1992 to 2016. The first-order Markov state-dependent transition model was preferred over random transition probabilities. Females that gave birth had, on average, an 85% chance of pupping in the following year. However, females that did not give birth had a 56% chance of giving birth in the following year, suggesting that female quality plays a role in breeding probability. Although breeding probability varied among years, there was no trend over time suggesting the average natality rate has not changed and is not contributing to the slowing of the rate of growth in pup production. [ABSTRACT FROM AUTHOR]

Diet estimation in marine mammals relies on indirect methods including recovery of prey hard parts from stomachs and feces, quantitative fatty acid signature analysis ( QFASA), stable isotope mixing models, and identification of prey DNA in stomach contents and feces. Experimental evidence (9 species/13 studies) shows that digestion strongly influences the proportion and size of otoliths that can be recovered in feces. Number correction factors ( NCF) and digestion coefficients have been experimentally determined to reduce the biases in fecal analysis. Correction factors and coefficients have not been determined for diet estimated from stomach contents. QFASA estimates which prey species and amounts must have been eaten to account for the fatty acid composition of the predator. Experimental studies on mammals and seabirds (9 species/10 studies) indicate that accurate estimates of diet can be determined using QFASA. Stable isotope mixing models provide rather coarse taxonomic resolution of diet composition. Prey DNA analysis shows promise as a method to estimate the species composition of diet, but further development and testing is needed to validate its use. Obtaining a representative sample from marine mammal populations is a significant challenge. Therefore, the use of complementary methods is recommended to obtain the most informative results. [ABSTRACT FROM AUTHOR]

Culling is widely practised as a means to reduce predation effects of terrestrial carnivores, birds and marine mammals in many parts of the world. Of marine mammals, coastal pinniped species have usually been the target of culling programs, but dolphins and a large odontocete have also been culled., We reviewed the published literature on marine mammal culling programs to evaluate the extent of their efficacy as a fisheries management measure., Changes in species' distributions and abundance demonstrate that culling programs can be very effective at reducing predator density., Several conclusions from experimental studies of terrestrial mammals and birds may also apply to marine mammal control. Firstly, predator removal generally increases productivity and population size of target prey populations, but not always. Secondly, culling programs typically involve a large proportional reduction (>50%) in predator populations., Thirdly, the effects of culling are typically dependent on continued control, and in the absence of control the population rapidly returns to pre-culling density. This underscores the need for predator removal to be a long-term management strategy. Fourthly, culling predators often has non-intuitive and unintended consequences for target species and for other predator and prey species., Marine mammal culling programs rarely have measurable objectives with respect to prey populations, and their success has not been evaluated. Culling marine mammals is controversial because of the following: (i) they are high-profile charismatic megafauna; (ii) many populations are recovering from a period of over-exploitation while others remain threatened or endangered; and (iii) the scientific evidence needed to justify a cull is usually highly uncertain., Marine mammal culling programs should be based on scientific analysis with stated and measurable objectives to be evaluated during planned follow-up monitoring. [ABSTRACT FROM AUTHOR]

We compared the behaviors of primiparous and multiparous gray seal (Halichoerus grypus) females over the course of lactation to examine whether poorly developed maternal behaviors may play a role in the reduced lactation performance observed in primiparous females. Overall, primiparous females spent as much time interacting with their pups as multiparous females. The proportion of time spent nursing their pup increased significantly between early and peak lactation in both primiparous and multiparous females. Although there was no significant difference in the duration of nursing bouts as a function of reproductive status, primiparous females nursed significantly more frequently (bouts/hour) and, therefore, spent a significantly greater proportion of time nursing than multiparous females throughout lactation. Primiparous gray seal females were also significantly more active than multiparous females, however, the difference in activity represented only a small proportion of the overall time budget. We conclude that poorly developed maternal behaviors resulting from a lack of prior reproductive experience are unlikely to account for lower levels of milk energy transfer to pups in primiparous gray seals. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented which discusses guidelines for the handling and treatment of marine mammals in field research to improve peoples' understanding of their behavior, physiology and life history.

Pup production on Sable Island, Nova Scotia, has been increasing exponentially since the early 1960s and by 1997 Sable Island was the largest gray seal colony worldwide. Using an aerial photographic survey, as in previous years, we estimated pup production in January 2004 to determine if this exponential rate of increase had continued. A total of 33,268 pups was counted on the color positives. When corrected for the proportion pups missed on the imagery (1.106 for the 12th; 1.527 on the 13th), the proportion of pups that died prior to the survey (0.031), and the proportion of pups born before the survey (east colony 0.966, west colony 0.962), estimated total pup production was 41,500 with SE = 4,381. The 2004 estimate indicates that pup production on Sable Island has continued to increase, but suggests that the rate of increase ( r) may have declined (0.070 compared to previous 0.128). Females from the 1998–2000 cohorts were about 16 times less likely to give birth for the first time at age 4 yr and more than twice as likely at age 6 yr compared to those in the mid-late 1980s. The new estimate of pup production and observed changes in age of primiparity provide the first indication of changes in vital rates of this population. However, additional estimates of pup production and vital rates are needed to confirm this conclusion and to investigate the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Studies using molecular markers have shown that some grey seal males may be gaining success through exhibiting alternative mating tactics. We estimated the probability of fertilization success of grey seal males exhibiting the primary tactic of female defence and one alternative tactic of mating with departing females on Sable Island, Nova Scotia, Canada, during the breeding seasons of 1997–2002. Although the fertilization rate of the primary tactic (27–43%) was greater than that of the alternative tactic (10–12%), these low rates indicate the potential fitness value of alternative mating tactics in this size-dimorphic pinniped species. [ABSTRACT FROM AUTHOR]