Lake Erie walleyes Sander vitreus support important fisheries and have been managed as one stock, although preliminary tag return and genetic analyses suggest the presence of multiple stocks that migrate among basins within Lake Erie and into other portions of the Great Lakes. We examined temporal and spatial movement and abundance patterns of walleye stocks in the three basins of Lake Erie and in Lake St. Clair with the use of tag return and sport and commercial catch-per-unit effort (CPUE) data from 1990 to 2001. Based on summer tag returns, western basin walleyes migrated to the central and eastern basins of Lake Erie and to Lake St. Clair and southern Lake Huron, while fish in the central and eastern basins of Lake Erie and in Lake St. Clair were primarily caught within the basins where they were tagged. Seasonal changes in sport and commercial effort and CPUE in Lake Erie confirmed the walleye movements suggested by tag return data. Walleyes tagged in the western basin but recaptured in the central or eastern basin of Lake Erie were generally larger (or older) than those recaptured in the western basin of Lake Erie or in Lake St. Clair. Within spawning stocks, female walleyes had wider ranges of movement than males and there was considerable variation in movement direction, minimum distance moved (mean distance between tagging sites and recapture locations), and mean length among individual spawning stocks. Summer temperatures in the western basin often exceeded the optimal temperature (20-238C) for growth of large walleyes, and the
Since 1990, walleyes Sander vitreus in Lake Erie have been tagged annually with jaw tags to better understand the population dynamics and ecological characteristics of individual spawning populations. Although the data collected from this tagging program have been used for a variety of management purposes (e.g., estimating migration patterns, stock intermixing, and mortality rates), there has been only cursory examination of the shedding and reporting rates associated with the program. We used double tagging and high-reward tagging experiments to estimate tag shedding and reporting rates for jaw-tagged walleyes in Lake Erie. Double tagging of walleyes with jaw and passive integrated transponder (PIT) tags suggested that the tagging method and tagging agency contributed to the observed variability in both immediate (within 21 d of tagging) retention and chronic jaw tag shedding rates. Agency-specific model-averaged estimates of immediate tag retention ranged from 95% to 99%. For chronic shedding, model-averaged instantaneous rates (annual) ranged from 0.07 to 0.28. Jaw tag reporting rates, estimated via releases of high-reward tags in 1990 and 2000, varied among tagging years, tagging basins, and commercial and recreational fisheries. In general, tag reporting rates were higher for the recreational fishery (range, 33-55%) than for the commercial fishery (10-17%),
Background: Intracoelomic implantation of electronic tags has become a common method in fishery research, but rarely are fish examined by scientists after release to understand the extent that surgical incisions have healed. Walleye (Sander vitreus) are a valuable, highly exploited fishery resource in the Laurentian Great Lakes. Here, fishery capture of walleye with internal acoustic transmitters combined with a high reward program provided multiple opportunities to examine photographs and quantify the status of surgical incisions. Walleye (n = 926) from reef and river spawning populations in Lake Erie and Lake Huron were implanted with acoustic transmitters during spring spawning events from 2011 to 2016. Incisions were closed with polydioxanone monofilament using two to three interrupted sutures. Out of 276 recaptured fish, 60 incision sites were clearly visible in photographs, and these were scored by two independent readers for incision closure, inflammation, and the presence of sutures.Results: While incision sites were completely closed by 61 days post-release (95% CI 44-94), sutures remained for up to 866 days. Sutures were expelled serially during a protracted period, and the probability of observing at least one suture in a recaptured fish declined below 50% after 673 days (95% CI 442-1016). Inflammation at the incision increased during the first 71 days and then declined monotonically, remaining detectable at low levels. Conclusion:Our results emphasized that sutures remained in free-ranging fish past the time when they were beneficial for incision healing. Most dissolvable sutures have been designed for use in endotherms where the body temperature and internal milieu differ dramatically from the conditions experienced by fishes in temperate climates. Identification of new suture materials for fish that facilitate healing while absorbing or dissolving in a reasonable period (e.g., a few weeks to three months) in colder temperatures (e.g., <12 °C) would be beneficial to mitigate potential adverse impacts from inflammation at the incision.
Maturation schedules, key determinants of fish stocks' harvest potential and population dynamics, are influenced by both plastic and adaptive processes. Various indices are used to describe maturation schedules, and these have differential advantages for discriminating between plastic and adaptive processes. However, potential sampling‐related biases associated with different maturation indices have not been fully evaluated. We analyzed three maturation indices for walleyes Sander vitreus in Lake Erie; Saginaw Bay, Lake Huron; and Oneida Lake, New York: age and length at 50% maturity, midpoint of age‐specific maturity ogives (age‐specific length at which probability of maturity = 0.50), and midpoints of probabilistic maturation reaction norms (PMRNs; age‐specific length at which probability of maturing in the following year = 0.50). We then compared estimated maturation indices to evaluate sensitivity of different maturation indices to sampling‐induced biases and to assess the relative importance of plastic versus adaptive processes in structuring interstock and temporal variation in maturation schedules. Our findings suggest that although small changes in sampling month, gear, and agency‐related effects can bias estimates of age and length at 50% maturity and midpoints of maturity ogives, PMRN estimates appear to be robust to these biases. Furthermore, PMRN estimates are suggestive of potential adaptive variation in maturation schedules among walleye stocks and over time. For instance, Oneida Lake walleyes (which had relatively slow growth and low mortality rates) matured at a smaller size for a given age (smaller midpoints of PMRNs) than the other stocks. Temporally, walleyes in the western basin of Lake Erie matured at a larger size in recent years, as evidenced by increasing midpoints of PMRNs (1978–1989 versus 1990–2006 for Ohio Department of Natural Resources data and 1990–1996 versus 1997–2006 for Ontario Ministry of Natural Resources data). Our study highlights the necessity of monitoring maturation schedules via multiple maturation indices and the need to account for sampling‐induced biases when comparing maturation schedules.
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