The complexity and cost of assessment techniques prohibits their application to 90% of fisheries. Simple generic approaches are needed for the world's small-scale and data-poor fisheries. This ...meta-analysis of the relationship between spawning potential and the normalized size and age of 123 marine species suggests that the so-called Beverton-Holt life-history invariants (BH-LHI; L sub(m)/L sub( infinity ), M/k, M Age sub(m)) actually vary together in relation to life-history strategy, determining the relationship between size, age, and reproductive potential for each species. Although little realized, the common assumption of unique values for the BH-LHI also implies that all species share the same relationship between size, age, and reproductive potential. This implicit assumption is not supported by this meta-analysis, which suggests that there is considerable but predictable natural variation in the BH-LHI ratios and the relationships between size, age, and reproductive potential that they determine. We believe that this reconceptualization of the BH-LHI has potential to provide a theoretical framework for "borrowing" knowledge from well-studied species to apply to related, unstudied species and populations, and when applied together with the assessment technique described by Hordyk et al. (2015b), could make simple forms of size-based assessment possible for many currently unassessable fish stocks.
The potential for hatchery-release programs to augment the harvest rates of fisheries can be limited by environmental factors associated with survival, growth and body condition among released ...individuals. We assessed spatial and temporal variability in the condition of postlarval and small juvenile (1–10 mm carapace length) eastern king prawnsPenaeus plebejusHess sampled from an estuarine population subjected to pilot releases of 3 million postlarvae per year in southeastern Australia. Variability in the length–weight relationship was used as a measure of condition and compared between (1) autumn/winter and spring/summer periods and (2) bare and macrophytic habitats forP. plebejussampled from a population in a closed estuarine system. At a reference carapace length of 3.97 mm, condition was ~14% higher for individuals sampled from bare habitat and ~16% higher for those sampled during autumn/winter compared, respectively, with individuals sampled within macrophytic habitat and during spring/summer. Further experimental work on the factors investigated here is encouraged to increase our understanding of the environmental characteristics and mechanisms that lead to improved condition and thus persistence of stocked populations ofP. plebejus.
Carbon and nitrogen stable isotope ratios of three estuarine autotrophs (the seagrass,
Zostera capricorni and its epiphytic algae, and the saltcouch grass
Sporobolus virginicus) were measured within ...and among sites in Southern Moreton Bay, Southeast Queensland. For all taxa, isotope ratios were significantly affected by the position of a plant within a site. Carbon signatures of
S. virginicus were more enriched at upper elevations (−14.3‰), and more depleted at the lower edge (−15.0‰). Small but significant differences for
S. virginicus were also found between edge (−14.7‰) and interior (−14.9‰) positions.
Z. capricorni was more depleted in
15
N
at edge (5.9‰) positions than the interior (6.2‰). The seagrass epiphytes varied along the elevation gradient, being more depleted in
13
C
at the upper (−19.7‰) than the lower (−19.3‰) edge. This small within-site variation (< 1‰) may result from differences in the physical characteristics among the sites that influence the productivity of plants and thereby their isotope ratios, but would not preclude the use of carbon and nitrogen stable isotopes in small-scale food web studies. At a larger scale, isotope ratios differed significantly among sites separated by several kilometres and the range of this variation was greater for all taxa than at the within-site scale. Differences among sites are probably due to variation in nutrient source and hydrodynamics.
A bioeconomic model was developed to evaluate the potential performance of brown tiger prawn stock enhancement in Exmouth Gulf, Australia. This paper presents the framework for the bioeconomic model ...and risk assessment for all components of a stock enhancement operation, i.e. hatchery, grow-out, releasing, population dynamics, fishery, and monitoring, for a commercial scale enhancement of about 100 metric tonnes, a 25% increase in average annual catch in Exmouth Gulf. The model incorporates uncertainty in estimates of parameters by using a distribution for the parameter over a certain range, based on experiments, published data, or similar studies. Monte Carlo simulation was then used to quantify the effects of these uncertainties on the model-output and on the economic potential of a particular production target. The model incorporates density-dependent effects in the nursery grounds of brown tiger prawns. The results predict that a release of 21
million 1
g prawns would produce an estimated enhanced prawn catch of about 100
t. This scale of enhancement has a 66.5% chance of making a profit. The largest contributor to the overall uncertainty of the enhanced prawn catch was the post-release mortality, followed by the density-dependent mortality caused by released prawns. These two mortality rates are most difficult to estimate in practice and are much under-researched in stock enhancement.
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