Variation in Life History of Fishes: Accounting for and Incorporating Spatiotemporal Variability in Demographic Rates (hosted by AFS)

The life history traits and demographic parameters of many fish species show considerable variation across both space and time. Factors such as climate, habitat, oceanographic features, conspecific density, or local diversity may influence rates of growth, maturity, and fecundity. However, the corresponding effects of such variability on stock productivity and sustainable fisheries management largely remain unknown. Despite the fact that the theoretical basis for variable life history traits is relatively well established and has a long history of use in predicting population demography, there remains a clear need for both mechanistic studies that determine the drivers of life history variability, as well as for studies that focus on how to best incorporate this information into management frameworks such as stock assessments, defining essential fish habitat, population viability analyses, and integrated ecosystem assessments. The purpose of this symposium is to assemble researchers who study the patterns, mechanisms, and consequences of life history variability in order to better define spatiotemporal dynamics across species, habitats, and ecosystems. We hope this symposium will advance the state of the science of life history variability in fishes, and highlight the key elements and processes required to advance these ideas into the management arena. This session is sponsored by the Fish Habitat Section.

8:20AM Spatial and Temporal Variability in Growth of Mutton Snapper
  Robert Ellis, Jessica Carroll
Accurately determining the variability of key life history parameters is an essential part of sustainably managing fisheries. Growth rates in fish may vary across both time and space and these variations may significantly alter estimates of stock productivity and the expectations for population trajectories and associated harvest quotas. We examined over 15,000 otolith-determined ages of Mutton Snapper (Lutjanus analis) that were caught by both commercial and recreational fishers across four decades along the Florida Atlantic and Gulf coasts. We examined these age-length records for decadal and regional differences in derived von Bertalanffy growth model parameters. We found that Mutton Snapper growth parameters differed significantly across decades and between regions. Specifically, the highest growth rates (K) were found in the 1990s while the largest maximum size estimates (Linf) occurred in the 2000s. Regionally, fish from the Atlantic coast had the highest growth rates, while the largest maximum size estimates were found for fish from the northeastern Gulf of Mexico, and both Atlantic and Gulf estimates differed from those for fish caught in south Florida. These results will inform future research into the causes and consequences of variable growth in Mutton Snapper.
8:40AM Oceanographic Features Influence the Spatiotemporal Distributions of Early Life Stages of Small Tuna Species (Euthynnus alletteratus and Thunnus atlanticus) in the Oceanic Gulf of Mexico
  Nina Pruzinsky, Rosanna Milligan, Tracey Sutton
Tunas are ecologically important in pelagic ecosystems, but due to their economic value in commercial and recreational fisheries, tunas are overfished. Declines in large-tuna fisheries in the Gulf of Mexico (GoM) are expected to directly increase fishing pressures on unmanaged, small tuna species (e.g., little tunny, Euthynnus alletteratus, and blackfin tuna, Thunnus atlanticus), whose ecology and life history traits are relatively unknown. Juveniles represent the life stage that is more likely to survive to adulthood than larvae; however, distributional studies on juveniles are rare, leading to a gap in our understanding of tuna ecology. Tuna early life stages were collected across the GoM from December 2010-September 2011 (NOAA-supported Offshore Nekton Sampling and Analysis Program) and in May and August from 2015-2017 (GOMRI-supported DEEPEND Consortium). Generalized additive models and distributional plots indicated that early life stages of E. alletteratus were associated with productive continental shelf/slope environments (low salinity, high chlorophyll a concentrations, nearer to shelf break), while T. atlanticus juveniles were associated with oligotrophic habitats (high salinity, low chlorophyll a concentrations, further from shelf break). Integrating physical oceanographic features and quantitative abundance estimations of juvenile tunas across a broad spatiotemporal domain is critical for management and conservation efforts for small tunas.
9:00AM Reproductive Life History of Yelloweye Rockfish (Sebastes ruberrimus) in Prince William Sound and the Northern Gulf of Alaska
  Donald Arthur, Jeff Falke, Anne Beaudreau, Trent M. Sutton, Brittany Blain
Rockfish are characterized by slow growth, late maturity, and low natural mortality rates. These life history characteristics are especially pronounced in Yelloweye Rockfish (Sebastes ruberrimus), which has contributed to the species’ overfished status throughout its southern range from California to British Columbia. Northern stocks in Alaska are presumed to be healthy, but there is a lack of critical information on life history characteristics and no stock assessments have been conducted for this species in this region. The goal of this project is to generate estimates of important reproductive parameters for Yelloweye Rockfish in Prince William Sound and the northern Gulf of Alaska and compare to information throughout the species range. We collected biological data and gonads from Yelloweye Rockfish in Prince William Sound during 2018-2019. Sexual maturity values were assigned through histological examination of gonadal tissue. A Bayesian hierarchical model fit with a logistic function predicted the posterior mean age (years; A50) and fork length (cm; L50) at 50% maturity to be 18.56 years and 43.8 cm, respectively. Although L50 was similar to southern populations, A50 was younger than predicted based on latitude. This life history information will be important to estimating reproductive potential and stock assessment modeling.
9:20AM Differences in Life History Effects on Population Responses to Environmental Variability: Atlantic Cod Gadus Morhua As an Example
  Mikaela Provost, Louis W. Botsford
Life histories of Atlantic cod vary widely, causing substantial differences in the sensitivity of populations to fishing, as well as population responses to annual variability in their environments. Previous work on Atlantic cod shows that life-histories of populations in warmer regions of the Northeast Atlantic Ocean are better able to sustain higher fishing rates than those in the cooler Northwest. Cohort resonance shows how life history acts as a filter of environmental noise such that populations can be more sensitive to environmental change over: 1) very long and 2) generational timescales, thus populations with different life histories exposed to the same environment will exhibit different patterns of temporal variability. One key question is what aspects of cod life history determine the different amounts of sensitivity at these two timescales? We use stochastic age-structured models to describe time scales of sensitivity for 16 cod populations in the North Atlantic. We show that all cod populations are more sensitive to variability on long time scales (i.e., low frequencies), but few show the sensitivity to variability at periods near one generation (i.e., high frequencies) seen in other species and, when are present they tend to appear in populations with high peak spawning ages.
09:40AM Break
10:10AM Food Webs and Salmonid Life History across a Mediterranean Gradient.
  Gabriel Rossi, Shelley Pneh, Weston Slaughter, Keane Flynn, Mary Power, Ted Grantham
Food Webs and Salmonid Life History across a Mediterranean Gradient The seasonality of food webs and hydraulic conditions exert a strong effect on the life history of rearing juvenile salmonids, particularly in Mediterranean streams – characterized by strong inter- and intra-annual hydrologic variability. However, the term “Mediterranean stream” encompasses a wide range of hydrologies from perennial to nearly arid systems. This study investigates how the foraging behavior, physiology, and life history of juvenile steelhead (Oncorhynchus mykiss) track food web and hydrologic phenology in two radically different Mediterranean streams – one perennial and the other intermittent. Late-spring growth potential was higher in the intermittent stream, but conditions favorable to growth declined sharply to an inhospitable low DO environment with high fish mortality by mid-summer. In the perennial stream growth was steady, with low mortality even in late summer. The life history implication for anadromous salmonids between these streams are pronounced, with strong differences in foraging phenology, apparent lipid allocation, and outmigration constraints. The contribution of juveniles from these different streams to a meta-population of steelhead may represent a juvenile portfolio effect which could buffer the population to patterns of ocean survival and interannual hydrologic variability.
10:30AM Do Lake-Specific Characteristics Mediate the Temporal Relationship between Walleye Growth and Warming Water Temperature?
  Danielle Massie, Yan Li, Gretchen Hansen, Tyler Wagner
Quantifying the drivers of spatiotemporal variability in fish growth is necessary for predicting species’ response to environmental changes. In particular, it is important to understand how warming water temperature influence growth, and whether ecosystem properties may mediate the growth-temperature relationship. Our objectives were to: 1) quantify the spatiotemporal variability of Walleye growth in Minnesota and Wisconsin lakes, 2) determine if annual growth coefficient estimates (K) are correlated with growing degree days (GDD), and 3) identify if lake characteristics are drivers of the K-GDD relationship. To calculate spatiotemporal growth variability, we fitted a Bayesian hierarchical von Bertalanffy growth model to Walleye length-at-age data from 1993-2015 for 25 lakes. Growth estimates were found to vary substantially among years and lakes. We predict that northern lakes with cooler water temperatures will have a positive K-GGD relationship, while southern lakes may have a negative relationship due to temperatures potentially reaching beyond the optimal temperature for Walleye growth. Additionally, we hypothesize that deeper lakes may help mitigate the influence of warming water temperatures, while fish in shallower lakes may be more affected by warming water temperatures. This study will provide insights into the conservation of cool-water species subjected to a changing environment.
10:50AM Field-Based Evidence of Latent Effects on Lake Erie Walleye Growth Rates
  L. Zoe Almeida, Matthew Faust, Stuart A. Ludsin, Elizabeth A. Marschall
Growth rates are generally assumed to be responses to recent environmental conditions; however, evidence shows that growth during one year may also reflect environmental conditions experienced earlier in life. We examined which early-life factors influence growth rates of Lake Erie Walleye (Sander vitreus) using data from annual gillnet surveys (1978-2015) to characterize median size-at-age of cohorts from ages 3 to 5 (i.e., young adults). For females, percent ice cover during February-March, which immediately precedes the hatching period, was the only early-life factor correlated with later growth rates. Percent ice cover during the year of hatching was positively correlated with growth in young female adults (pseudo R2 = 0.54). For males, median body size at age-2 and whether the annual cohort originated before or after 1987 were the important early-life factors: 1) median size at age-2 was positively correlated with growth; 2) cohorts produced during 1987-2015 had the fastest growth; and 3) cohorts produced before 1987 had a steeper relationship between size at age-2 and growth (pseudo R2 = 0.39). Our analyses demonstrate that early-life experiences may have lingering influences on adult Walleye growth. We are currently using structural equation modeling to identify the mechanisms that might be underlying these correlations.
11:10AM State-Space Models for Estimating Sub-Population Diversity in Mixed-Stock Pacific Salmon Fisheries
  Ben Staton, Matthew Catalano, Brendan Connors, Michael L. Jones, Carl Walters, Steven J. Fleischman, Daniel Gwinn
Sub-populations harvested in mixed-stock Pacific salmon fisheries show diversity in genotypic, behavioral, and life history characteristics. Methods to quantify heterogeneity in sub-population intrinsic productivity (which might result from these factors) are not well-established, yet estimates are required for full acknowledgement of trade-offs when setting harvest policies. We developed an integrated age-structured state-space framework for simultaneously estimating Ricker parameters of multiple sub-populations in a mixed-stock. This model allows for more complete use of available data and sharing of information than methods that would fit individual models to each sub-population. Alternative state-space model structures were developed and were compared to simpler regression-based approaches. The models were fitted to reconstructed data from 13 Chinook Salmon sub-populations in the Kuskokwim River in western Alaska as a case study. Biological and policy conclusions were found to be largely consistent between state-space model structures, but differed strongly from regression-based approaches. Simulation trials showed that the state-space models were largely unbiased with respect to leading parameters, abundance states, and derived biological reference points, whereas the regression-based approaches provided spuriously too aggressive management advice. These findings suggest the state-space model shows promise for populating harvest policy evaluations in the context of harvest-biodiversity trade-offs in mixed-stock salmon fisheries.

Organizers: Robert Ellis, Jessica Carroll, Joshua Kilborn
Supported by: AFS Fish Habitat Section

Location: Reno-Sparks CC Date: October 2, 2019 Time: 8:20 am - 11:50 am