Demographic characteristics of exploited tropical lutjanids: a comparative analysis

Demographic parameters from seven exploited coral reef lutjanid species were compared as a case study of the implications of intrafamily variation in life histories for multispecies harvest management. Modal lengths varied by 4 cm among four species (Lutjanus fulviflamma, L. vitta, L. carponotatus, L. adetii), which were at least 6 cm smaller than the modal lengths of the largest species (L. gibbus, Symphorus nematophorus, Aprion virescens). Modal ages, indicating ages of full selection to fishing gear, were 10 years or less for all species, but maximum ages ranged from 12 (L. gibbus) to 36 years (S. nematophorus). Each species had a unique growth pattern, with differences in length-at-age and mean asymptotic fork length (L∞), but smaller species generally grew fast during the first 1–2 years of life and larger species grew more slowly over a longer period. Total mortality rates varied among species; L. gibbus had the highest mortality and L. fulviflamma, the lowest mortality. The variability in life history strategies of these tropical lutjanids makes generalizations about lutjanid life histories difficult, but the fact that all seven had characteristics that would make them particularly vulnerable to fishing indicates that harvest of tropical lutjanids should be managed with caution

Lessons learned from practical approaches to reconcile mismatches between biological population structure and stock units of marine fish

Recent advances in the application of stock identification methods have revealed inconsistencies between the spatial structure of biological populations and the definition of stock units used in assessment and management. From a fisheries management perspective, stocks are typically assumed to be discrete units with homogeneous vital rates that can be exploited independently of each other. However, the unit stock assumption is often violated leading to spatial mismatches that can bias stock assessment and impede sustainable fisheries management. The primary ecological concern is the potential for overexploitation of unique spawning components, which can lead to loss of productivity and reduced biodiversity along with destabilization of local and regional stock dynamics. Furthermore, ignoring complex population structure and stock connectivity can lead to misperception of the magnitude of fish productivity, which can translate to suboptimal utilization of the resource. We describe approaches that are currently being applied to improve the assessment and management process for marine fish in situations where complex spatial structure has led to an observed mismatch between the scale of biological populations and spatially-defined stock units. The approaches include: (i) status quo management, (ii) "weakest link" management, (iii) spatial and temporal closures, (iv) stock composition analysis, and (v) alteration of stock boundaries. We highlight case studies in the North Atlantic that illustrate each approach and synthesize the lessons learned from these real-world applications. Alignment of biological and management units requires continual monitoring through the application of stock identification methods in conjunction with responsive management to preserve biocomplexity and the natural stability and resilience of fish species.</p

Empirical Legal Studies Before 1940: A Bibliographic Essay

The modern empirical legal studies movement has well-known antecedents in the law and society and law and economics traditions of the latter half of the 20th century. Less well known is the body of empirical research on legal phenomena from the period prior to World War II. This paper is an extensive bibliographic essay that surveys the English language empirical legal research from approximately 1940 and earlier. The essay is arranged around the themes in the research: criminal justice, civil justice (general studies of civil litigation, auto accident litigation and compensation, divorce, small claims, jurisdiction and procedure, civil juries), debt and bankruptcy, banking, appellate courts, legal needs, legal profession (including legal education), and judicial staffing and selection. Accompanying the essay is an extensive bibliography of research articles, books, and reports

Variation in the population biology of stripey bass Lutjanus carponotatus within and between two island groups on the Great Barrier Reef

Density, population structure, mortality and growth of Lutjanus carponotatus on the Great Barrier Reef were compared on 2 spatial scales: between the Lizard and Palm Island groups and among 4 locations within the Palm group. The mean density at the Palm group was approximately 7 times that of the Lizard group. There were 2-fold differences in density within the Palm group, but strong statistical signals were not detected due to high variability in the data. Differences in size structures and asymptotic body sizes between the island groups were pronounced, and smaller differences were also evident within the Palm group. While age structures were similar among Palm group locations and lacked anomalous peaks, a series of strong cohorts at older age classes at the Lizard group suggests greater recruitment variability there during the past 2 decades. Variability in mortality did not increase with scale, as larger differences existed within the Palm group than between it and the Lizard group. The population traits estimated in this study were used in conjunction with reef area data to generate estimates of abundance and biomass, the values of which illustrate how multiple population traits interact to ultimately determine population size and reproductive potential. Multi-scale studies that examine a variety of aspects of population biology are rare for large reef fish, but are needed to identify which traits are likely to exhibit variation on which spatial scales

Stock structure, mortality and growth of the decorated goby, Istigobius decoratus (Gobiidae), at Lizard Island, Great Barrier Reef

Gobiids are an abundant component of coral reef ichthyofauna, yet little is known of their life histories. I examined population structure, mortality and growth of the decorated goby, Istigobius decoratus, a common gobiid of shallow patch reefs on the Great Barrier Reef. Presumed daily increments in sagittal otoliths were used as a proxy for age. The upper age estimate was 266 days suggesting at most an annual life cycle. Instantaneous natural mortality rate estimates were 5.92 year⁻¹ and 7.92 year⁻¹ using two estimators, both corresponding to less than 1% annual survivorship. Specimens ranged from 12 to 84 mm total length. Analysis of size-at-age data indicated linear growth at a rate of 0.33 mm day⁻¹. The linear relationship between size and age meant the population size structure mirrored the age structure with both skewed toward the smallest and youngest classes. High mortality over a 1-year longevity and linear growth suggest high population turnover and, therefore, that I. decoratus and ecologically similar species serve a potentially important role as prey species. This suite of traits is rarely reported for coral reef fishes, which is probably due to the limited attention paid to small-bodied species rather than the rarity of such a life history in these communities

Sex-specific growth and mortality, spawning season, and female maturation of the stripey bass (Lutjanus carponotatus) on the Great Barrrier Reef

Sex-specific demography and reproductive biology of stripey bass (Lutjanus carponotatus) (also known as Spanish flag snapper, FAO) were examined at the Palm and Lizard island groups, Great Barrier Reef (GBR).Total mortality rates were similar between the sexes. Males had larger L∞ at both island groups and Lizard Island group fish had larger overall L∞. Female:male sex ratios were 1.3 and 1.1 at the Palm and Lizard island groups, respectively. The former is statistically different from 1, but is unlikely significantly different in a biological sense. Females matured on average at 2 years of age and 190 mm fork length at both locations. Female gonadal lipid body indices peaked from August through October, preceding peak gonadosomatic indices in October, November, and December that were twice as great as in any other month. However, ovarian staging revealed 50% or more ovaries were ripe from September through February, suggesting a more protracted spawning season and highlighting the different interpretations that can arise between gonad weight and gonad staging methods. Gonadosomatic index increases slightly with body size and larger fish have a longer average spawning season, which suggests that larger fish produce greater relative reproductive output. Lizard Island group females had ovaries nearly twice as large as Palm Island group females at a given body size. However, it is unclear whether this reflects spatial differences akin to those observed in growth or effects of sampling Lizard Island group fish closer to their date of spawning. These results support an existing 250 mm minimum size limit for L. carponotatus on the GBR, as well as the timing of a proposed October through December spawning closure for the fishery. The results also caution against assessing reef-fish stocks without reference to sex-, size-, and location-specific biological traits

Demographic variation within spatially structured reef fish populations: when are larger-bodied subpopulations more important?

Environmental heterogeneity frequently induces spatial variability in somatic growth, which can cause inter-population differences in reproductive output among organisms for which fecundity is dependent upon body size. Mean asymptotic body size, L∞, varies among populations of several reef fish species. Deterministic models suggest L∞ has little effect on population growth, so subpopulations with larger L∞ may not have disproportionate effects in sustaining an open system. We used a stochastic simulation model to examine the potential role of a larger L∞ subpopulation in aspects of population dynamics beyond population growth under a range of assumptions about the prevailing recruitment relationships. We compared dynamics of a demographically homogeneous system with a system that included one subpopulation with 20% larger L∞. Despite the magnitude of the increase in L∞, mean population size and average time at large population sizes differed little between the homogenous system and that with the larger L∞ subpopulation. However, including the larger L∞ subpopulation did result in less time spent at very small population sizes, which could reduce extinction risks. Effects of the larger L∞ subpopulation were most pronounced when a deterministic recruitment cycle was imposed in combination with high stochastic variability in recruitment. This was due to regular series of poor recruitment years shifting the population structure toward older cohorts where differences in body size (and reproductive output) between the larger L∞ subpopulation and the other subpopulations were greatest. Differences were also greater when recruitment variability was regionally correlated. When recruitment variability was locally independent, the probability of system-wide declines was reduced because declines of individual populations at one time were replenished by unaffected neighbors in subsequent years. Our study suggests that variation in L∞ within a network of interconnected subpopulations may not be an important determinant of population behavior under certain conditions, but might be important in coping with periods of persistent, system-wide recruitment failure

Metapopulation ecology in the sea: from Levins' model to marine ecology and fisheries science

Marine and fisheries scientists are increasingly using metapopulation concepts to better understand and model their focal systems. Consequently, they are considering what defines a metapopulation. One perspective on this question emphasizes the importance of extinction probability in local populations. This view probably stems from the focus on extinction in Levins' original metapopulation model, but places unnecessary emphasis on extinction–recolonization dynamics. Metapopulation models with more complex structure than Levins' patch-occupancy model and its variants allow a broader range of population phenomena to be examined, such as changes in population size, age structure and genetic structure. Analyses along these lines are critical in fisheries science, where presence–absence resolution is far too coarse to understand stock dynamics in a meaningful way. These more detailed investigations can, but need not, aim to assess extinction risk or deal with extinction-prone local populations. Therefore, we emphasize the coupling of spatial scales as the defining feature of metapopulations. It is the degree of demographic connectivity that characterizes metapopulations, with the dynamics of local populations strongly dependent upon local demographic processes, but also influenced by a nontrivial element of external replenishment. Therefore, estimating rates of interpopulation exchange must be a research priority. We contrast metapopulations with other spatially structured populations that differ in the degree of local closure of their component populations. We conclude with consideration of the implications of metapopulation structure for spatially explicit management, particularly the design of marine protected area networks