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Assessing progress for the endangered white shark (Carcharodon carcharias) relative to Canadian conservation objectives requires understanding distribution patterns. From the largest tagging data set in the Northwest Atlantic (2010-2020; 272 deployments), we determined the proportion of the population detected in Canadian waters, characterized patterns in occupancy, and explored the behavioural characteristics of animals while in Canadian waters versus elsewhere in their range. The component of the population detected in Canadian waters annually was highly variable, yet proportionately small. Juveniles and subadults were 4.7 and 3.4 times more likely, respectively, to move northward than adults. From June to November, all pop-up satellite archival tagged white sharks remained primarily in coastal locations within the 200 m bathymetric contour and exhibited shallow diving behaviour within the top 100 m of the water column. However, individuals in Canadian waters experienced a more restricted temperature range and used proportionately less of the water column. Accounting for behavioural effects on distribution when predicting habitat use from environmental associations will become critical to evaluate the population-level impact of recovery actions implemented under Canadian legislation. Key words: conservation, telemetry, white shark, distribution, dive behaviour, Northwest Atlantic L'evaluation des progres en ce qui concerne le grand requin blanc (Carcharodon carcharias), une espece en voie de disparition, par rapport aux objectifs de conservation canadiens necessite une comprehension de ses motifs de repartition. A la lumiere du plus important ensemble de donnees de marquage pour l'Atlantique Nord-Ouest (2010-2020, 272 deploiements), nous avons determine la proportion de la population detectee dans les eaux canadiennes, caracterise les motifs d'occupation et compare les caracteristiques comportementales d'individus alors qu'ils etaient presents en eaux canadiennes et ailleurs dans leur aire de repartition. La composante de la population detectee en eaux canadiennes annuellement est tres variable, bien que proportionnellement faible. Les juveniles et subadultes sont, respectivement, 4,7 et 3,4 fois plus susceptibles de se deplacer vers le nord que les adultes. De juin a novembre, tous les requins blancs dotes d'etiquettes satellites autodetachables a archivage demeurent principalement dans des sites littoraux a l'interieur de la courbe bathymetrique de 200 m et presentent un comportement de plongee peu profonde dans les 100 premiers metres de la colonne d'eau. Les individus dans les eaux canadiennes sont cependant exposes a une fourchette de temperatures plus restreinte et utilisent une moins grande proportion de la colonne d'eau. La prise en compte d'effets comportementaux sur la repartition dans la prediction de l'utilisation d'habitats a partir d'associations environnementales sera d'importance cle pour l'evaluation de l'incidence a l'echelle des populations de mesures de retablissement mises en oeuvre en vertu de la legislation canadienne. [Traduit par la Redaction] Mots-cles : conservation, telemetrie, grand requin blanc, repartition, comportement de plongee, Atlantique Nord- Ouest, Introduction Abiotic conditions are considered to be the predominant factors shaping pelagic shark distributions, where modeling typically uses water temperature or related characteristics of the water column to describe or [...]

Context: For threatened marine species, data on their vertical habitat use patterns can reveal risk of interactions with fishing gear and can inform bycatch avoidance strategies. Such data are lacking for young porbeagles (Lamna nasus), which are captured as bycatch in north-western Atlantic fisheries. Aims: We aimed to examine temporal patterns in diving and characterise vertical habitat use of young porbeagles during summer and autumn. Methods: We used data from short-term (28-day), high-resolution (5-min interval) pop-off satellite tags attached to 14 young (young-of-the-year and 1-year-old) porbeagles to model depth use. Key results: Occupied depths ranged from the sea surface to 679 m, with ambient water temperatures of −0.2 to 26°C. Diel period and season were factors related to depth use. Conclusions: Sharks exhibited a diel activity pattern characterised by more extensive use of the water column during the day while remaining primarily at the surface at night. Depth use differed between seasons, with summer characterised by greater affinity for surface waters (0–10 m) compared to autumn. Implications: Young porbeagles are at risk of interaction with active fisheries on the continental shelf, but interactions may be reduced by setting gear deeper at night or during summer. The depth use of young porbeagles was investigated for the first time during the summer and autumn in the north-western Atlantic. Depth use varied on both daily and seasonal scales, with sharks occupying surface waters during the night and summer, and diving deeper during the day and autumn. Results can inform bycatch reduction strategies for this vulnerable life stage. [ABSTRACT FROM AUTHOR]

Abstract: 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 [...]

The North Atlantic Designatable Unit (DU) of Shortfin Mako Shark was assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Endangered in April 2019, and is currently under consideration for listing under Schedule 1 of the Species at Risk Act (SARA). The Recovery Potential Assessment (RPA) presented here provides information to support the listing recommendation and any recovery actions, should the species be listed. Shortfin Mako occurs throughout the Northern Hemisphere of the Atlantic Ocean. The biological characteristics of Shortfin Mako (i.e., relatively long lifespan, late maturity, and low reproductive output) make the population very susceptible to fishing pressure, which is the main threat identified in the North Atlantic. Multiple international and Canadian fisheries intercept Shortfin Mako as bycatch, and the most recent assessment of the DU predicts that it is overfished relative to biomass at Maximum Sustainable Yield (MSY). Reducing total removals in the North Atlantic to 500 mt is projected to have a > 50% probability of population recovery by 2070. For comparison, international and Canadian removals in 2019 totalled 1,863 mt and 63 mt, respectively. Considering just Canadian fleets, interception probabilities are highest from pelagic longline, with an average of 48% of observed sets encountering Shortfin Mako, followed by bottom longline (0.4% of sets) and otter trawl (0.2% of sets). The most effective Canadian mitigation measure for Shortfin Mako will be the new landings prohibition, implemented in 2020 for pelagic longline and scheduled for implementation in 2021 for fixed-gear groundfish fisheries. The effectiveness of other mitigation measures are relatively unclear and, in many cases, would require dedicated experimentation to test. The current requirement to use circle hooks may need to be revised due to new evidence that increased catchability outweighs any reduction in post-release mortality for Shortfin Mako, thus leading to greater total mortality as compared to using J-hooks. Given the current level of international fisheries removals and the extent of mitigation already in place in Canada, there is very little scope for mitigation actions by Canada to measurably affect recovery potential. [ABSTRACT FROM AUTHOR]

Typically, juvenile survey data are not used explicitly to determine status, trends, or abundance designations for Atlantic salmon Salmo salar, even though they can be the only source of information for many populations. To determine whether juvenile data can be informative about adult abundance and status in Atlantic salmon, we evaluated the similarities in trends among age-classes for two data-rich populations using a nested log-linear model. We found relatively consistent and significant trends for the age-0, adult and egg time series, but the trends in juvenile density data for older age-classes were less consistent with adult abundance trends. A threshold-based analysis demonstrated that relatively low misclassification rates for adult status relative to a set reference level could be obtained from juvenile density estimates. Together, these results suggest that juvenile density data can be an informative proxy for adult abundance and may be useful as an indicator for large changes in population status relative to reference points. This would make data collection via electrofishing an appropriate monitoring method for fisheries management or conservation programs. However, the validity of the idea that dramatic changes in adult abundance will be mirrored in juvenile data partially depends on the specific age-classes monitored, the survey design, and the timing of density dependence in the population. Using juvenile data as an index would necessitate some prior knowledge of the underlying population dynamics before the method could be applied more generally. [ABSTRACT FROM AUTHOR]