Monthly Archives: May 2018

Ideas on evaluating the value of monitoring data and the vulnerability of management advice to data degradation on the US West Coast

Kristin Marshall1
1NWFSC
May 29th, 2018 9:00 (PST): FSH 105

Ideas on evaluating the value of monitoring data and the vulnerability of management advice to data degradation on the US West Coast

The costs and values of monitoring is an important consideration for natural resource management. For example, fishery independent surveys are financially demanding. Yet, sound advice for fisheries management relies on high quality survey data. On the West Coast, most stock assessment models use indices of abundance and age composition data from surveys to estimate biomass available to fisheries and inform decisions about harvest levels. Static or declining federal budgets translate to fewer dollars available to conduct fishery independent surveys. NWFSC currently faces difficult decisions about allocation of resources among surveys. In order to minimize the impact of potential reductions in survey funding and make better decisions about allocating funding, understanding the consequences of reduced survey data on assessment models is a key challenge. Recent work by the NWFSC assessment team investigated retrospective scenarios that reduced survey data by 50%, which, among other impacts, could have led to triggering the “40-10” control rule for several rockfish species. Using that study as motivation, in this talk, I will discuss (and solicit) ideas for expanding on that work with potential approaches to 1) identify target species whose management is likely vulnerable to changes in survey effort, 2) better demonstrate the costs and values of fisheries independent surveys, and 3) provide advice on how to lessen the effects of reduced budgets for monitoring.

Characterizing sources of uncertainty in future projections of the Eastern Bering Sea food web using a multi species-size spectrum model

Jonathan Reum1
1NWFSC
May 08, 2018 9:00 (PST): FSH 105

Characterizing sources of uncertainty in future projections of the Eastern Bering Sea food web using a multi species-size spectrum model

In this talk I’ll give an overview of my ongoing efforts to (1) calibrate and validate a multi-species size spectrum model of the Eastern Bering Sea and (2) generate future projections of the EBS food web using 11 different downscaled global climate model (GCM) projections. The size spectrum model can represent different hypothesized pathways through which climate may influence system dynamics. Specifically, temperature can influence predator feeding rates and natural morality and the productivity of low trophic level groups can also be modified in accordance with down-scaled estimates for the EBS using each GCM. While there are several potential sources of structural and parameter uncertainty that may influence the projection envelope, I focus on how projection uncertainty is apportioned according to GCM, climate impact hypothesis, and fishing mortality scenario over time. In a preliminary simulation experiment, near-term projection uncertainty (2020 – 2050) of biomass for some species (e.g., forage fish, snow crab, pollock) was dominated by uncertainty related to fishing mortality scenario. However, uncertainty stemming from GCMs and the specific climate hypothesis was more important for long-term (2075-2100) projection uncertainty. The reverse pattern was observed for other species (e.g., Pacific cod, Pacific halibut). I’ll discuss how this information can be useful for prioritizing future research and and developing ensemble projections. This modeling work is part of the Alaska Climate Integrated Modeling Project (ACLIM).