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.

Biological parameters of the Atlantic sharpnose shark Rhizoprionodon terraenovae in the northern Gulf of Mexico were re-examined to test for potential changes due to density dependent responses. Biological data from published studies in the Gulf of Mexico collected during the period 1979–1984 were compared with data collected during the period 1998–2001. For combined sexes, the von Bertalanffy growth parameters were L 8 = 110.8 cm total length, K = 0.39 year–1 and t o = –0.86 year during 1984 and L 8 = 94.0 cm total length, K = 0.73 year–1 and t o = –0.88 year during 1998–2001. Median size for males and females at maturity decreased from approximately 78.3 and 80.2 cm total length (TL), respectively, in 1979–1980 to 72.6 and 75.8 cm TL, respectively, in 1998–2001. Age at maturity for combined sexes also decreased from 2.3 years in 1979–1980 to 1.4 years in 1998–2001. Litter size was similar between periods (5.0 embryos), as was the average size of embryos close to parturition (32 cm TL; 130–150 g). Growth rates using observed mean size-at-age data were higher from 1998–2001 for early ages (0–2.5 years). The observed decrease in maturity and increased growth rate lends support to the hypothesis of a compensatory response, although it could not be fully determined whether the response was due to differences in methodology among studies, anthropogenic influences or natural causes.

The true state of ocean biodiversity is difficult to assess, and there are few global indicators to track the primary threat of overfishing. We calculated a 50-year Red List Index of extinction risk and ecological function for 1199 sharks and rays and found that since 1970, overfishing has halved their populations and their Red List Index has worsened by 19%. Overfishing the largest species in nearshore and pelagic habitats risks loss of ecomorphotypes and a 5 to 22% erosion of functional diversity. Extinction risk is higher in countries with large human coastal populations but lower in nations with stronger governance, larger economies, and greater beneficial fisheries subsidies. Restricting fishing (including incidental catch) and trade to sustainable levels combined with prohibiting retention of highly threatened species can avert further depletion, widespread loss of population connectivity, and top-down predator control.

In 2003, the U.S. distinct population segment of smalltooth sawfish Pristis pectinata was listed as endangered under the U.S. Endangered Species Act (ESA). At that time, little was known about its habitat use patterns and, although required as part of the ESA, critical habitat could not be officially designated. Subsequently, studies were conducted that identified some of the specific habitats and environmental conditions important for the species. Facilitating recruitment into the adult population by protecting the species’ nurseries was identified in the recovery plan as the key conservation objective, which would be supported by the designation of critical habitat. The location of nurseries was determined by applying published criteria developed for identifying elasmobranch nursery areas to a decade of encounter data. These largely nontraditional data were composed primarily of encounters voluntarily reported by the public to members of the recovery team. The nursery habitats essential to the conservation of the species were identified as those adjacent to red mangroves Rhizophora mangle and euryhaline habitats with water depths ≤0.9 m. Ultimately, two broad areas in southwest Florida that contain these habitats were designated as critical habitat for juvenile smalltooth sawfish: the Charlotte Harbor Estuary unit (896 km²) and the Ten Thousand Islands/Everglades unit (2,505 km²). Received June 23, 2011; accepted March 12, 2012