Connectivity between white shark populations off Central California, USA and Guadalupe Island, Mexico

Marine animals often move beyond national borders and exclusive economic zones resulting in a need for trans-boundary management spanning multiple national jurisdictions. Highly migratory fish vulnerable to over-exploitation require protections at international level, as exploitation practices can be disparate between adjacent countries and marine jurisdictions. In this study we collaboratively conducted an analysis of white shark connectivity between two main aggregation regions with independent population assessment and legal protection programs; one off central California, USA and one off Guadalupe Island, Mexico. We acoustically tagged 326 sub-adult and adult white sharks in central California (n=210) and in Guadalupe Island (n=116) with acoustic transmitters between 2008-2019. Of the 326 tagged white sharks, 30 (9.20%) individuals were detected at both regions during the study period. We used a Bayesian implementation of logistic regression with a binomial distribution to estimate the effect of sex, maturity, and tag location to the response variable of probability of moving from one region to the other. While nearly one in ten individuals in our sample were detected in both regions over the study period, the annual rate of trans-regional movement was low (probability of movement = 0.015 yr-1, 95% credible interval = 0.002, 0.061). Sub-adults were more likely than adults to move between regions and sharks were more likely to move from Guadalupe Island to central California, however, sex, and year were not important factors influencing movement. This first estimation of demographic-specific trans-regional movement connecting US and Mexico aggregations with high seasonal site fidelity represents an important step to future international management and assessment of the northeastern Pacific white shark population as a whole

Circadian activity of the Wels catfish (Silurus glanis) in the Danube River

In this study, the movements and behaviour of Wels catfish (Silurus glanis, Linnaeus, 1758) were monitored during the different seasons when the water level in the river changed significantly. Wels catfish was caught on the Danube River, rkm 863, and tagged with an ultrasonic transmitter. Deployed Vemco receivers recorded detections of spatial movement between years 2015 and 2017. Our telemetry data found relatively short movements within a maximum range (~12km), but as a territorial species most of the time it was recorded by the two receivers, close to the Iron Gate dam and location where it was caught. Circadian rhythm showed that in the summer period, nocturnal activity is evident while during winter Wels catfish stayed most of the time at the same depth under the water surface. Wels catfish changed depths during the autumn and spring when more activity was recorded. The last signal received was during the winter 2017, which was period with the low temperatures and ice cover on the Danube River. This research shows the value and importance of installing coded acoustic transmitters in fish and monitoring their movement using a series of autonomous receivers deployed in the Danube River. Research by telemetry can be used to better understand fish behaviour and movements and to help improve large river management measures

Connectivity between white shark populations off Central California, USA and Guadalupe Island, Mexico

Marine animals often move beyond national borders and exclusive economic zones resulting in a need for trans-boundary management spanning multiple national jurisdictions. Highly migratory fish vulnerable to over-exploitation require protections at international level, as exploitation practices can be disparate between adjacent countries and marine jurisdictions. In this study we collaboratively conducted an analysis of white shark connectivity between two main aggregation regions with independent population assessment and legal protection programs; one off central California, USA and one off Guadalupe Island, Mexico. We acoustically tagged 326 sub-adult and adult white sharks in central California (n=210) and in Guadalupe Island (n=116) with acoustic transmitters between 2008-2019. Of the 326 tagged white sharks, 30 (9.20%) individuals were detected at both regions during the study period. We used a Bayesian implementation of logistic regression with a binomial distribution to estimate the effect of sex, maturity, and tag location to the response variable of probability of moving from one region to the other. While nearly one in ten individuals in our sample were detected in both regions over the study period, the annual rate of trans-regional movement was low (probability of movement = 0.015 yr-1, 95% credible interval = 0.002, 0.061). Sub-adults were more likely than adults to move between regions and sharks were more likely to move from Guadalupe Island to central California, however, sex, and year were not important factors influencing movement. This first estimation of demographic-specific trans-regional movement connecting US and Mexico aggregations with high seasonal site fidelity represents an important step to future international management and assessment of the northeastern Pacific white shark population as a whole

Videos to BEH 3810

   Video 1. Slow straight-line swimming (Table 1, Section 3.1.2). Video 2. Self-body cleaning (Table 1, Section 3.1.10). Video 3. Courtship and Copulation (Table 2, Sections 3.2.8–3.2.12, 3.2.15, 3.2.18). Video 4a. Basking shark ram feeding on plankton (Table 3, Section 3.3.1). Video 4b. Reef manta rays ram feeding on plankton (Table 3, Section 3.3.6). Video 5. Saw Bite (Table 4, Section 3.4.5). Video 6. Vertical breach with prey seizure (Table 5, Section 3.5.4). Video 7. Horizontal bite and lateral head shake (Table 5, Sections 3.5.6, 3.5.8–3.5.9). Video 8. Scavenging on sea lion (Table 5, Section 3.5.14). Video 9. Schooling (Table 6, Section 3.6.7). Video 10. Swim by (Table 6, Section 3.6.10). Video 11. Aggressive behaviours (Table 7, Sections 3.7.2, 3.7.4–3.7.5, 3.7.7–3.7.8) Video 12. Tail slap (Table 7, Section 3.7.10). Video 13. Exaggerated tail beats and looping (Table 7, Section 3.7.12). Video 14. Reflex biting (Table 7, Section 3.7.24). Video 15. Anti-predatory biting (Table 8, Section 3.8.5).</p