Ecology and conservation of long-lived marine animals

Long-lived marine animals generally have slow growth and late maturity. In addition, many long-lived species have low fecundity or variable and infrequent recruitment. Long life span may be an evolutionary adaptation to promote iteroparity and maintain fitness. Long-lived marine animals tend to be particularly vulnerable to excessive mortalities and rapid stock collapse, after which recovery may take decades. The von Bertalanffy growth coefficient (k) is a useful index in addressing the potential vulnerability of stocks to excessive mortality. Groups that have k coefficients at or below 0.10 seem to be particularly vulnerable and include most elasmobranchs, most chondrichthians, some teleosts, and the cheloniid sea turtles. Another useful index in assessing the vulnerability of stocks to excessive mortality is the intrinsic rate of increase (r). Vulnerability is inversely proportional to rwith groups that have annual increase rates less than 10% being particularly at risk. These include most elasmobranchs, most chondrosteans, some teleosts, all sea turtles, many sea birds, and large cetaceans. Traditional surplus production models may be inappropriate for most long-lived marine animals because of the long lag time in population response to harvesting. Rather, demographic models based on life history parameters have provided useful recently in assessing impacts of mortality on long-lived species. The greatest threats to long-lived marine animals come from mixed species fisheries in which long-lived species are taken ancillary to more abundant, productive species. Such fisheries may reduce long-lived species to critical levels while the more productive species sustain catches. Resource managers need to be more aware of the critical management requirements of long-lived marine animals. In most instances such species can sustain only limited excess mortality. To ignore the special nature of the population dynamics of long-lived species leads inevitably to stock collapse or even extirpation.