Thomas F Ihde

Ecosystem-based management (EBM) of the ocean considers all impacts on and uses of marine and coastal systems. In recent years, there has been a heightened interest in EBM tools that allow testing of alternative management options and help identify tradeoffs among human uses. End-to-end ecosystem modeling frameworks that consider a wide range of management options are a means to provide integrated solutions to the complex ocean management problems encountered in EBM. Here, we leverage the global advances in ecosystem modeling to explore common opportunities and challenges for ecosystem-based management, including changes in ocean acidification, spatial management, and fishing pressure across eight Atlantis (atlantis.cmar.csiro.au) end-to-end ecosystem models. These models represent marine ecosystems from the tropics to the arctic, varying in size, ecology, and management regimes, using a three-dimensional, spatially-explicit structure parametrized for each system. Results suggest stronger impacts from ocean acidification and marine protected areas than from altering fishing pressure, both in terms of guild-level (i.e., aggregations of similar species or groups) biomass and in terms of indicators of ecological and fishery structure. Effects of ocean acidification were typically negative (reducing biomass), while marine protected areas led to both “winners” and “losers” at the level of particular species (or functional groups). Changing fishing pressure (doubling or halving) had smaller effects on the species guilds or ecosystem indicators than either ocean acidification or marine protected areas. Compensatory effects within guilds led to weaker average effects at the guild level than the species or group level. The impacts and tradeoffs implied by these future scenarios are highly relevant as ocean governance shifts focus from single-sector objectives (e.g., sustainable levels of individual fished stocks) to taking into account competing industrial sectors' objectives (e.g., simultaneous spatial management of energy, shipping, and fishing) while at the same time grappling with compounded impacts of global climate change (e.g., ocean acidification and warming).

Abstract.—Aging structures for spotted seatrout Cynoscion nebulosus have been compared for the first time by using sectioned pectoral fin rays, sectioned dorsal fin spines, scales, and whole and sectioned otoliths from 50 fish of 300 to 731 mm total length. We considered the ...

Despite increasing importance of marine recreational fisheries, management goals and objectives have not changed from a focus on managing for commercially important objectives such as maximum or optimum sustainable yield. Additionally, recreational fishery stakeholders in several prominent U.S. fisheries have been frustrated by a perceived lack of inclusion of recreational views in fishery management decisions. Our objective was to provide

Being aware of model parameter and structure uncertainty is necessary for understanding the expected outcome of management actions. Methods of dealing with model uncertainty are disparately applied around the Chesapeake Bay research and resource management community. The communication of these concepts and study results to managers is likewise disparate. Models are important as frameworks for identifying management priorities and research needs. Models are needed to understand the populations and to simplify the complex dynamics of ecosystems that the decision-makers seek to manage. Research studies and monitoring performed can ultimately help to reduce the parameter and structure uncertainty in model outputs. Thus, the most effective use of models and their results will both help managers understand the dynamics of the resources that they manage and identify research priorities that will improve the precision of model results; ideally, this process improves the reliability of model...

The Atlantis ecosystem modeling approach is an end-to-end simulation, integrating system information from array of disciplines and data at a variety of scales. The approach complements existing stock assessment approaches by linking geophysical information, watershed nutrient dynamics, habitat studies, and fish and invertebrate population dynamics to fisheries production. With results from simulations of the Chesapeake Atlantis Model, we discuss how the loss of marsh habitat in the Chesapeake Bay is predicted to affect Chesapeake populations, and what the consequences may be for ocean production of those species that rely on the largest estuary in the US.

ABSTRACT Indices of recruitment are often derived from trap surveys. If legal-sized lobsters inhibit smaller ones from entering traps this can cause a bias in estimated trends with serious management consequences. Recruitment strength can be overestimated as average length decreases in a population. A controlled field experiment was used to examine whether trapping inhibition of Jasus edwardsii occurred during spring (November) or summer (February) in southeastern Tasmania. Four treatments were applied. Baited traps were seeded with either: one large female lobster, one large male or two sublegal-sized females. Baited traps with no seed were used as a control. Seeded traps always caught fewer sublegal-sized lobsters than control traps. When catches in both seasons were examined by sex of the entrants, seeded traps caught fewer small lobsters than control traps in 11 of 12 comparisons. However, a strong inhibitory effect was observed only for female-seeded traps during summer. Our data suggest a sublegal-sized index of recruitment is likely to be influenced in summer by the number of large females present. Spring trials suggest that corrections to a sublegal-catch index may be unnecessary then, but more work is needed to better understand the complex, sex-specific and seasonal patterns of interactions in this species.

ABSTRACT The index-removal (IR) method provides estimates of abundance, exploitation rate and survey catchability based on the change in catch rate between pre- and post-harvest surveys. However, model estimates often demonstrate poor precision. A multiple-year IR model (1qIR) was developed to improve the precision of model estimates. Both the multiple-year and single-year models were applied to simulated data to compare model performance over a range of exploitation rates, and to test 1qIR model robustness to failure of the assumption of constant catchability over all years. Both models were then applied to data from a southern rock lobster fishery in Tasmania, Australia. The 1qIR model consistently outperformed the single-year model in all chosen performance criteria using simulated data and data from the rock lobster fishery. The performance of the 1qIR model continued to improve as additional years were added to the dataset. When the survey catchability coefficient varied in 1 of 5 years, the 1qIR model was robust to failure of the assumption of constant catchability among years until a 50% change in catchabilities occurred. When applied to rock lobster fishery data, 1qIR estimates were less variable than single-year model estimates and provided reasonable estimates of population abundance, survey catchability coefficient, and exploitation rate. Diagnostic tests to evaluate model estimates of exploitation rate were described and applied to model estimates for parameters of the rock lobster fishery. The 1qIR model estimates performed well in diagnostic plots, but results for the single-year model were poor. The 1qIR model offers a useful method to estimate abundance and exploitation rate in situations when estimates from the single-year model prove too variable to be useful.

ABSTRACT Change-in-ratio (CIR) and index-removal (IR) methods can be used to estimate exploitation rate when a survey is conducted before and after a harvest. When the magnitude of the harvest is also known, it is possible to estimate the abundance and the survey catchability coefficient. We present three diagnostic procedures for evaluating whether the assumptions of constant catchability appear reasonable. We show for the CIR method that it is not necessary to assume the two defined groups (generally, legal, and sublegal size animals) have equal catchability: if sublegal size animals are unexploited the estimated exploitation rate for the legal size group is unbiased. The assumption for the CIR method that the ratio of survey catchabilities of the two size groups does not vary over time can be evaluated by comparing the size composition of sublegal size animals over time in the surveys. For the IR method, the assumption that survey catchability remains constant over time can be evaluated by comparing the catch rates of sublegal sized animals before and after the fishing season. The assumption that all animals have the same catchability at a point in time, necessary for the IR method, can be evaluated by estimating the population separately by size group and comparing the sum of the population estimates with the estimate of the total population computed from all of the data; this requires that the harvest be known by size group. Data from the southern rock lobster fishery in Tasmania are used to illustrate these techniques.