Various biases and limitations associated with mark-recapture research have resulted in conflicting interpretations of individual movement patterns, rendering unclear the selective pressures that could be responsible for structuring populations and influencing individual behavior patterns in the marine environment. To address these issues, novel modeling techniques developed for mammalian systems were applied to trajectory data from an American lobster Homarus americanus population in order to describe quantitatively seasonal movement patterns. Basing individual-and population-level analyses on a correlated random walk model, individuals were found to belong to 1 of 2 movement types: residents or dispersers. Over the course of a year, resident animals remained in the general area of their release, whereas dispersing animals moved rapidly away from release sites in autumn and slowly returned in spring. Such movement patterns can be explained as responses to seasonal limitations in hard-substrate habitat. The effect of movement on the seasonal population distribution and structure of lobsters can have significant consequences for the sustainable exploitation of the species.

Supplementation programs based on captive breeding and rearing are increasingly being used in recovery planning for endangered or threatened salmonid populations. However, it is largely unknown if increased abundance from these programs can offset deleterious genetic changes from the captive environment and lead to viable populations in the wild. In this paper, we developed a life‐history‐based population viability analysis that explicitly incorporates declines in fitness attributable to captive breeding and rearing using the breeder's equation as part of the projection model. Using endangered inner Bay of Fundy Atlantic salmon as a case study (a population assemblage for which supplementation is a major component for the recovery plan), we evaluated how genetic changes influence abundance trajectories and extinction risk. Based on the population projections, continual supplementation enables the population to build from critically low abundance levels, even under high rates of fitness loss. However, beyond 4–6 generations, loss of fitness (>15%) outweighs any increase in abundance and causes the population projection to start to decline. For the majority of the scenarios, abundances were predicted to increase and remain in excess of the current population size for 10 to upward of 30 years, albeit at progressively lower population‐level fitness as compared to current values. Although the captive breeding and rearing program does prevent extinction in the short term in this case study, associated fitness costs limit the population's overall probability of recovery, as well as increase the length of time to recovery. Under the assumption of interbreeding between wild and captive‐reared individuals, declines greater than 10% in relative fitness at a population level are sufficient to counter abundance increases resulting from supplementation. Although extinction risk over the short term can be reduced by increasing the proportion of the population that is reared in captivity, this comes at a cost to the probability of recovery for the population over the longer term, particularly as environmental conditions change. Generalizing from this case study, the useful duration of supplementation programs may be limited to short‐term population increase (i.e., to prevent extinction) and may not be a workable strategy for longer term recovery planning.

Metapopulation structure is typically thought to increase regional species abundance, promote population persistence, and aid in the re-establishment of extirpated populations. However, the underlying theoretical models tended to assume high productivity, making the conservation benefit of metapopulation structure uncertain for endangered species with low productivity. We simulated population assemblages (N = 50) of diadromous fishes under high to low productivity scenarios to explicitly assess how straying (movement from natal to non-natal rivers) contributes to changes in species abundance and extinction risk. The population aggregation exhibited greater total abundance from source–sink dynamics and also exhibited the rescue effect when productivity remained moderately high. However, straying did not ensure persistence of nonviable populations or enable population re-establishment when productivity was low. These results were robust to a wide range of alternate spatial and life-history parameterizations of the simulation model. Relative to a real-world population aggregation of endangered Atlantic salmon (Salmo salar), our results would argue for a shift in remediation priorities to prevent extinction. Although there is strong evolutionary justification for maintaining widespread distributions of endangered diadromous species, the immediate numerical consequences of this approach may hinder recovery.

We examined relationships between abundance and habitat use in three age classes of juvenile Atlantic salmon ( Salmo salar ) in the Stewiacke River, Nova Scotia, Canada. Using stream gradient as a proxy for habitat quality, we used a double half normal function, modified to include density dependence, to model the relationship between habitat quality and fish density. We found that density was asymmetrically distributed around a similar optimum gradient for all three age classes regardless of abundance. Habitat use was highly density-dependent for age-0 and age-1 juveniles, but not for age-2+ salmon. As abundance of age-0 and age-1 salmon increased, their relative density decreased in low-gradient habitat and increased in higher-gradient habitat, although their absolute density increased in all stream gradient categories. Variation in habitat use was consistent with ideal free theory for age-1 juveniles in high-gradient habitat, but not in low-gradient habitat. Age-2+ individuals appeared not to modify their distribution among habitats, even though increasing competition changes the relative benefit of low-gradient habitat in terms of resource acquisition. In contrast, age-1 individuals responded to increased competition by modifying their distribution along the habitat gradient, even though this may have slightly reduced an individual’s potential for growth.

To effectively protect at‐risk sharks, resource managers and conservation practitioners must have a good understanding of how fisheries removals contribute to changes in abundance and how regulatory restrictions may impact a population trajectory. This means they need to know the number of animals being removed from a population and whether a given number of removals will lead to population increases or declines. For white shark (Carcharodon carcharias), theoretical quantities like the intrinsic rate of population increase or rebound potential (ability to increase in size following decline) are difficult to conceptualize in terms of real‐world abundance changes, which limits our ability to answer practical management questions. To address this shortfall, we designed a simulation model to evaluate how our understanding of longevity and life history variability of white shark affects our understanding of population trends in the Northwest Atlantic. Then, we quantified the magnitude of removals that could have caused historical population declines, compared these to biologically based reference points, and explored the removal scenarios which would result in population increase. Our results suggest that removals on the order of 100s of juveniles per year could have resulted in population‐level declines in excess of 60% during the 1970s and 1980s. Conservation actions implemented since the 1990s would have needed to be nearly 100% effective at preventing fishing mortality in order for the population to double in abundance over the last 30 years. Total removals from all fleets needed to be exceptionally small to keep them below biological reference points for white shark in the Northwest Atlantic. The population's inherent vulnerability to fishing pressure reaffirms the need for restrictive national and international conservation measures, even under a situation of abundance increase.