The island of Jamaica is often cited as an example of how overfishing has dramatically reduced the sizes of coral reef fishes. To examine the change in fish sizes over a 36-year period, we analyzed data from systemati...The island of Jamaica is often cited as an example of how overfishing has dramatically reduced the sizes of coral reef fishes. To examine the change in fish sizes over a 36-year period, we analyzed data from systematic surveys conducted in 1977 and 2013/14 of the sizes and relative abundances of four common algae-grazing fishes in the shallow backreef habitats of Jamaica and Grand Cayman. The four species are: striped parrotfish (Scarus iseri), stoplight parrotfish (Sparisoma viride), ocean surgeon (Acanthurus tractus) and the blue tang (Acanthurus coeruleus). We predicted that all four species would be larger in Grand Cayman than in Jamaica in 1977 as well as in 2013/14, because Grand Cayman has been cited as having less fishing pressure than Jamaica. For the same reason, we expected all four species would have declined in size over the 36 years in Jamaica but not in Grand Cayman. Furthermore, we predicted that the compressed body shape of the ocean surgeon and the blue tang would have made them especially vulnerable to net and trap fishing compared to the two parrotfishes, and that accordingly the effects of overfishing would be greater in these two species. We rejected this hypothesis. The size distributions of the laterally compressed species changed significantly on both islands over the 36-year time span, although not as predicted. At both islands, the blue tangs shifted toward smaller sizes and the ocean surgeons shifted toward larger sizes. There were no size distribution changes detected in the two fusiform species. There was also no support for the prediction that the sizes of these four species were larger in Grand Cayman than in Jamaica during either time period.展开更多
Although Caribbean mixed-species herbivorous fish groups are an important component to the reef community by helping to crop algae that often overgrow and kill corals, little is known of how they organize their foragi...Although Caribbean mixed-species herbivorous fish groups are an important component to the reef community by helping to crop algae that often overgrow and kill corals, little is known of how they organize their foraging groups. In spite of a highly flexible membership, the basic structure of these groups consists of a “core species,” that leads the group and often is either the striped parrotfish (Scarus iserti) or the ocean surgeon (Acanthurus tractus). These species lead their groups to open areas where they feed largely on low profile turf algae. Other members prefer macro algae and are termed “associate species,” of which the two common species we studied were the stoplight parrotfish (Sparisoma viride) and the redband parrotfish (Sparisoma aurofrenatum). In spite of the large difference in group sizes between Jamaica and Grand Cayman Islands, the relationships between movement patterns and compositional changes were largely consistent. There was no support for the hypothesis that these dramatic and continuous group changes were related to foraging success. Instead, we speculated that these group changes perhaps were designed to maintain cohesion among a membership that was spread over a wide area. We also examined if associates species may be more than just passive followers of core species but rather instigated the attracting or the building of core groups. Both associate species do attract striped parrotfish in open areas and thus appear active in initiating mixed-species groups. Finally, given that associate species seem to derive little foraging benefit from following core species, we tested the hypothesis that associate species joined core groups to gain protection against predators. Associate species do not selectively join the larger groups of striped parrotfish but appear to join core species randomly and the groups they joined resembled the wide assortment of core groups available in the area. Thus, while associates may be joining core groups for protection, this protection was not based on sizes of core groups.展开更多
文摘The island of Jamaica is often cited as an example of how overfishing has dramatically reduced the sizes of coral reef fishes. To examine the change in fish sizes over a 36-year period, we analyzed data from systematic surveys conducted in 1977 and 2013/14 of the sizes and relative abundances of four common algae-grazing fishes in the shallow backreef habitats of Jamaica and Grand Cayman. The four species are: striped parrotfish (Scarus iseri), stoplight parrotfish (Sparisoma viride), ocean surgeon (Acanthurus tractus) and the blue tang (Acanthurus coeruleus). We predicted that all four species would be larger in Grand Cayman than in Jamaica in 1977 as well as in 2013/14, because Grand Cayman has been cited as having less fishing pressure than Jamaica. For the same reason, we expected all four species would have declined in size over the 36 years in Jamaica but not in Grand Cayman. Furthermore, we predicted that the compressed body shape of the ocean surgeon and the blue tang would have made them especially vulnerable to net and trap fishing compared to the two parrotfishes, and that accordingly the effects of overfishing would be greater in these two species. We rejected this hypothesis. The size distributions of the laterally compressed species changed significantly on both islands over the 36-year time span, although not as predicted. At both islands, the blue tangs shifted toward smaller sizes and the ocean surgeons shifted toward larger sizes. There were no size distribution changes detected in the two fusiform species. There was also no support for the prediction that the sizes of these four species were larger in Grand Cayman than in Jamaica during either time period.
文摘Although Caribbean mixed-species herbivorous fish groups are an important component to the reef community by helping to crop algae that often overgrow and kill corals, little is known of how they organize their foraging groups. In spite of a highly flexible membership, the basic structure of these groups consists of a “core species,” that leads the group and often is either the striped parrotfish (Scarus iserti) or the ocean surgeon (Acanthurus tractus). These species lead their groups to open areas where they feed largely on low profile turf algae. Other members prefer macro algae and are termed “associate species,” of which the two common species we studied were the stoplight parrotfish (Sparisoma viride) and the redband parrotfish (Sparisoma aurofrenatum). In spite of the large difference in group sizes between Jamaica and Grand Cayman Islands, the relationships between movement patterns and compositional changes were largely consistent. There was no support for the hypothesis that these dramatic and continuous group changes were related to foraging success. Instead, we speculated that these group changes perhaps were designed to maintain cohesion among a membership that was spread over a wide area. We also examined if associates species may be more than just passive followers of core species but rather instigated the attracting or the building of core groups. Both associate species do attract striped parrotfish in open areas and thus appear active in initiating mixed-species groups. Finally, given that associate species seem to derive little foraging benefit from following core species, we tested the hypothesis that associate species joined core groups to gain protection against predators. Associate species do not selectively join the larger groups of striped parrotfish but appear to join core species randomly and the groups they joined resembled the wide assortment of core groups available in the area. Thus, while associates may be joining core groups for protection, this protection was not based on sizes of core groups.
