German Eel Model (GEM II) for describing eel, Anguilla anguilla (L.), stock dynamics in the river Elbe system

The eel, Anguilla anguilla (L.), stock of the river Elbe severely decreased during the last decades. Detailed knowledge of the stock dynamics in freshwater and especially of the impact factors is necessary to take effective measures for stock conservation and improvement. The dynamics of the eel stock are modelled based on immigration, stocking, natural mortality and mortalities caused by fishing, angling, cormorants and hydropower plants. The model estimates the number of emigrating eel. Moreover, it enables to study the sensitivity of the estimates related to the uncertainty of the source data of the different influencing factors. The model may be used to develop management strategies and to assess the effi ciency of different management options. Zusammenfassung Der Aalbestand im Elbesystem ist in den letzten Jahrzehnten stark zur

Coastal resource planning system: Integrating evaluation of ecological integrity and ecosystem services valuation

Efficient and effective coastal management decisions rely on knowledge of the impact of human activities on ecosystem integrity, vulnerable species, and valued ecosystem services—collectively, human impact on environmental quality (EQ). Ecosystem-based management (EBM) is an emerging approach to address the dynamics and complexities of coupled social-ecological systems. EBM “is intended to directly address the long-term sustainable delivery of ecosystem services and the resilience of marine ecosystems to perturbations” (Rosenberg and Sandifer, 2009). The lack of a tool that integrates human choices with the ecological connections between contributing watersheds and nearshore areas, and that incorporates valuation of ecosystem services, is a critical missing piece needed for effective and efficient coastal management. To address the need for an integrative tool for evaluation of human impacts on ecosystems and their services, Battelle developed the EcoVal™ Environmental Quality Evaluation System. The EcoVal system is an updated (2009) version of the EQ Evaluation System for Water Resources developed by Battelle for the U.S. Bureau of Reclamation (Dee et al., 1972). The Battelle EQ evaluation system has a thirty-year history of providing a standard approach to evaluate watershed EQ. This paper describes the conceptual approach and methodology of the updated EcoVal system and its potential application to coastal ecosystems. (PDF contains 4 pages)

A simulation model of the dynamics of Peruvian anchoveta (Engraulis ringens)

The article describes the key elements of a model simulating the dynamics of the anchoveta (Engraulis ringens) in the Peruvian upwelling system (4 degrees to 14 degrees South). This model, based on coupled differential equations, is parametrized mainly using empirical data and functional relationships presented in two volumes issued by ICLARM in 1987 and 1989, and may thus be viewed as test of the hypotheses presented therein. Results to date suggest that present knowledge of mechanisms controlling the anchoveta stock is essentially consistent, and sufficient to build a model reflecting essential features of the stock biomass and recruitment dynamics.

The effects of size-selective fisheries on the stock dynamics of and sperm limitation in sex-changing fish

Fisheries models have traditionally focused on patterns of growth, fecundity, and survival of fish. However, reproductive rates are the outcome of a variety of interconnected factors such as life-history strategies, mating patterns, population sex ratio, social interactions, and individual fecundity and fertility. Behaviorally appropriate models are necessary to understand stock dynamics and predict the success of management strategies. Protogynous sex-changing fish present a challenge for management because size-selective fisheries can drastically reduce reproductive rates. We present a general framework using an individual-based simulation model to determine the effect of life-history pattern, sperm production, mating system, and management strategy on stock dynamics. We apply this general approach to the specific question of how size-selective fisheries that remove mainly males will impact the stock dynamics of a protogynous population with fixed sex change compared to an otherwise identical dioecious population. In this dioecious population, we kept all aspects of the stock constant except for the pattern of sex determination (i.e. whether the species changes sex or is dioecious). Protogynous stocks with fixed sex change are predicted to be very sensitive to the size-selective fishing pattern. If all male size classes are fished, protogynous populations are predicted to crash even at relatively low fishing mortality. When some male size classes escape fishing, we predict that the mean population size of sex-changing stocks will decrease proportionally less than the mean population size of dioecious species experiencing the same fishing mortality. For protogynous species, spawning-per-recruit measures that ignore fertilization rates are not good indicators of the impact of fishing on the population. Decreased mating aggregation size is predicted to lead to an increased effect of sperm limitation at constant fishing mortality and effort. Marine protected areas have the potential to mitigate some effects of fishing on sperm limitation in sex-changing populations.

Fishery dynamics of the California market squid (Loligo opalescens), as measured by satellite remote sensing

Novel data on the spatial and temporal distribution of fishing effort and population abundance are presented for the market squid fishery (Loligo opalescens) in the Southern California Bight, 1992−2000. Fishing effort was measured by the detection of boat lights by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). Visual confirmation of fishing vessels by nocturnal aerial surveys indicated that lights detected by satellites are reliable indicators of fishing effort. Overall, fishing activity was concentrated off the following Channel Islands: Santa Rosa, Santa Cruz, Anacapa, and Santa Catalina. Fishing activity occurred at depths of 100 m or less. Landings, effort, and squid abundance (measured as landings per unit of effort, LPUE) markedly declined during the 1997−98 El Niño; landings and LPUE increased afterwards. Within a fishing season, the location of fishing activity shifted from the northern shores of Santa Rosa and Santa Cruz Islands in October, the typical starting date for squid fishing in the Bight, to the southern shores by March, the typical end of the squid season. Light detection by satellites offers a source of fine-scale spatial and temporal data on fishing effort for the market squid fishery off California, and these data can be integrated with environmental data and fishing logbook data in the development of a management plan.