Variable variability: difficulties in estimation and consequences for fisheries management

Recent analyses propose that the key regulatory processes in fisheries are stochastic, characterized by increased recruitment variance at low stock sizes (heteroscedasticity). Here, we investigate the consequences of this idea, with the aim of testing its practical relevance to fisheries management. We argue that stock‐recruitment time series are at least one order of magnitude too short to reliably fit heteroscedastic models; indeed, they are typically insufficient even to establish in which direction recruitment variance changes with stock size. Unreliable estimates of heteroscedasticity can have important management implications, depending on the sign of the coefficient of heteroscedasticity. Maximum sustainable yield (MSY) estimates from simple models, which include heteroscedasticity can be volatile, unrealistically high and sometimes non‐existent, as illustrated by an analysis of North Sea cod (Gadus morhua) data. In contrast, for North Sea herring (clupea harengus) data, heteroscedasticity has a negligible effect on MSY estimates. Statistical models are useful to elucidate broad‐scale regulatory processes, but will need to combined with the mechanistic understanding offered by models of population dynamics before being applied in a management setting.     

Dietary effect of squid and fish meals on growth and survival of Pacific white shrimp Litopenaeus vannamei in the presence or absence of phytoplankton in an indoor tank system

This study was conducted in 36 indoor 40‐L fibreglass aquaria to determine the weight gain and survival of Litopenaeus vannamei fed different dietary levels of fish (FM) and squid meal (SM) and to evaluate the potential of phytoplankton to reduce FM and SM levels in shrimp feeds. Six experimental isonitrogenous (35% protein) and isocaloric (17.5 kJ g^?1) diets were formulated to contain either 5%, 10% or 20% SM combined with either 6.5% or 12% FM. Dietary effects on growth and survival were compared in two systems: a ‘CLEAR water system’ (CWS) without the presence of microalgae and a ‘GREEN water system’ (GWS) with microalgae in the culture water. Shrimp cultured in the GWS had 28–57% greater weight gain than those cultured in the CWS, regardless of dietary treatment. However, survival was not different. Shrimp cultured in the CWS or the GWS, and fed diets containing combinations of FM and SM did not show differences in weight gain and feed conversion ratio. These results suggest that under the conditions existing during this research, 6.5% FM and 5% SM can be used as a cost‐effective combination in commercial feeds for shrimp production and that growth can be enhanced in the presence of primary productivity.     

Evaluation of chitosan and alginate immobilized Methylobacterium oryzae CBMB20 on tomato plant growth

Methylobacterium oryzae CBMB20, a promising plant growth promoting bacteria (PGPB) and a biocontrol agent, was immobilized in different formulations such as wet chitosan, dry chitosan, wet alginate and dry alginate and were tested for tomato plant growth promotion. Chitosan solution (1.5%) with pH 5.5–6.0 and 90 min contact time was found optimal for immobilization. The chitosan formulations showed better entrapment efficiency and good degradability resistance apart from slow release of cells under prolonged incubation. Survivability of bacteria (80%) was observed in wet chitosan formulation even after 90 days of storage at 4°C. The spermosphere survival of bacteria was high in both dry and wet chitosan formulations applied soils even after 21 days under greenhouse conditions. While the alginate formulation degraded fully, partial degradation of chitosan formulation was observed even after 30 days, indicating its ability to support the survival of M. oryzae CBMB20 in soil. Plants inoculated with wet chitosan formulation registered 1.3 fold increase in the shoot and root length and dry weight compared to other treatments. Hence, chitosan formulation supporting better plant growth compared to alginate will be a better carrier for taking bacteria to the plant rhizosphere and thereby promote plant growth.