When identifying potential trophic cascades, it is important to clearly establish the trophic linkages between predators and prey with respect to temporal abundance, demographics, distribution, and diet. In the northwest Atlantic Ocean, the depletion of large coastal sharks was thought to trigger a trophic cascade whereby predation release resulted in increased cownose ray abundance, which then caused increased predation on and subsequent collapse of commercial bivalve stocks. These claims were used to justify the development of a predator-control fishery for cownose rays, the “Save the Bay, Eat a Ray” fishery, to reduce predation on commercial bivalves. A reexamination of data suggests declines in large coastal sharks did not coincide with purported rapid increases in cownose ray abundance. Likewise, the increase in cownose ray abundance did not coincide with declines in commercial bivalves. The lack of temporal correlations coupled with published diet data suggest the purported trophic cascade is lacking the empirical linkages required of a trophic cascade. Furthermore, the life history parameters of cownose rays suggest they have low reproductive potential and their populations are incapable of rapid increases. Hypothesized trophic cascades should be closely scrutinized as spurious conclusions may negatively influence conservation and management decisions.

Research on rare and threatened species is often limited by access to sufficient individuals to acquire information needed to design appropriate conservation measures. Using a combination of data from pop‐up archival transmitting (PAT) tags across multiple institutional programmes, movements and habitat use of endangered smalltooth sawfish, Pristis pectinata were determined for animals from southern Florida and the Bahamas. All P. pectinata (n = 12) generally remained in coastal waters within the region where they were initially tagged, travelling an average of 80.2 km from deployment to pop‐up location. The shortest distance moved was 4.6 km and the greatest 279.1 km, averaging 1.4 km day‐1. Seasonal movement rates for females were significantly different with the greatest movements in autumn and winter. Pristis pectinata spent the majority of their time at shallow depths (96% of their time at depths <10 m) and warm water temperatures (22–28°C). Given sawfish show a degree of site fidelity punctuated by limited migratory movements emphasizes the need for conservation and management of existing coastal habitats throughout the species’ range.Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Anthropogenic alterations to river systems, such as irrigation and hydroelectric development, can negatively affect fish populations by reducing survival when fish are routed through potentially dangerous locations. Non-physical barriers using behavioural stimuli are one means of guiding fish away from such locations without obstructing water flow. In the Sacramento-San Joaquin River Delta, we evaluated a bio-acoustic fish fence (BAFF) composed of strobe lights, sound and a bubble curtain, which was intended to divert juvenile Chinook salmon (Oncorhynchus tshawytscha) away from Georgiana Slough, a low-survival migration route that branches off the Sacramento River. To quantify fish response to the BAFF, we estimated individual entrainment probabilities from two-dimensional movement paths of juvenile salmon implanted with acoustic transmitters. Overall, 7.7% of the fish were entrained into Georgiana Slough when the BAFF was on, and 22.3% were entrained when the BAFF was off, but a number of other factors influenced the performance of the BAFF. The effectiveness of the BAFF declined with increasing river discharge, likely because increased water velocities reduced the ability of fish to avoid being swept across the BAFF into Georgiana Slough. The BAFF reduced entrainment probability by up to 40 percentage points near the critical streakline, which defined the streamwise division of flow vectors entering each channel. However, the effect of the BAFF declined moving in either direction away from the critical streakline. Our study shows how fish behaviour and the environment interacted to influence the performance of a non-physical behavioural barrier in an applied setting. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.