M. J. Hamel

Tag Retention of T-Bar Anchor Tags and Passive Integrated Transponder Tags in Shovelnose Sturgeon

Abstract Capture–recapture methods are commonly used to estimate population parameters when the necessary assumptions are met. One of the broadest assumptions of capture–recapture models is that tags are not lost. Therefore, one must understand tag retention to be able to adjust estimates if tag loss occurs. Our objectives were to (1) determine retention rates of T-bar anchor tags and passive integrated transponder (PIT) tags injected into the dorsal musculature of shovelnose sturgeon Scaphirhynchus platorynchus and (2) determine whether using an alternative PIT-tagging location (the operculum) and a new tagging procedure (cyanoacrylate [i.e., superglue] to seal the tag insertion point) provided higher retention. The T-bar tags had a retention rate of 100%; PIT tag retention, however, was more variable. Injection of PIT tags along the dorsal fin resulted in a retention rate of 73%, and tag loss was observed throughout the 98-d experiment. The application of cyanoacrylate did not appear to deter PIT tag lo...

Validation of Annuli Formation in Pectoral Fin Rays from Shovelnose Sturgeon in the Lower Platte River, Nebraska

AbstractFish age is commonly estimated by counting bands on calcified structures. Age estimates are used to calculate information on population dynamics such as growth, mortality, and recruitment. Pectoral fin rays are the most frequently used structure to age sturgeon species, yet little work has been done to validate annuli formation. We collected Shovelnose Sturgeon Scaphirhynchus platorynchus monthly from the lower Platte River, Nebraska, during 2011 and 2012 and removed the leading, left pectoral fin ray from each fish captured. We used marginal increment analysis to assess the validity of annual deposition of growth marks on pectoral fin rays. There were two complete cycles of increasing and decreasing increment values between March and November within each year. Mean marginal increments showed minimal peaks in March, July, and October followed by a decrease in increment length during April, September, and November. However, mean marginal increments were similar between months in both years. These r...

The Global Status of Freshwater Fish Age Validation Studies and a Prioritization Framework for Further Research

Age information derived from calcified structures is commonly used to estimate recruitment, growth, and mortality for fish populations. Validation of daily or annual marks on age structures is often assumed, presumably due to a lack of general knowledge concerning the status of age validation studies. Therefore, the current status of freshwater fish age validation studies was summarized to show where additional effort is needed, and increase the accessibility of validation studies to researchers. In total, 1351 original peer-reviewed articles were reviewed from freshwater systems that studied age in fish. Periodicity and age validation studies were found for 88 freshwater species comprising 21 fish families. The number of age validation studies has increased over the last 30 years following previous calls for more research; however, few species have validated structures spanning all life stages. In addition, few fishes of conservation concern have validated ageing structures. A prioritization framework, using a combination of eight characteristics, is offered to direct future age validation studies and close the validation information gap. Additional study, using the offered prioritization framework, and increased availability of published studies that incorporate uncertainty when presenting research results dealing with age information are needed.

Variability in Age Estimation Results in Ambiguity and False Understanding of Population Persistence

AbstractMortality, growth, and recruitment are the primary dynamic rate functions that regulate fish populations. Age data obtained from calcified structures can provide direct and indirect information needed for calculations of these metrics; therefore, knowledge of the fish population age structure is often coveted information. Unfortunately, potential sources of error exist in the form of subjectivity in interpretation of growth increments, inconsistent deposition of growth increments, and lack of validation in age-estimation processes. However, many sources of error are either not known or simply ignored, particularly for long-lived fishes. Therefore, we included a level of uncertainty in our age estimates of a periodic life history strategist, the Shovelnose Sturgeon Scaphirhynchus platorynchus, by incorporating variability in reader assignment of age. We used a bootstrapping procedure to generate a matrix of new age distributions and demonstrated how calculations of mortality varied as a result of r...

Spatially dynamic maternal control of migratory fish recruitment pulses triggered by shifting seasonal cues

Environmental regimes set the timing and location of early life-history events of migratory species with synchronised reproduction. However, modified habitats in human-dominated landscapes may amplify uncertainty in predicting recruitment pulses, impeding efforts to restore habitats invaluable to endemic species. The present study assessed how environmental and spawner influences modulate recruitment variability and persistence of the Missouri River shovelnose sturgeon (Scaphirhynchus platorynchus) under modified seasonal spawning and nursery habitat conditions. Using a spatially explicit individual-based biophysical model, spawning cycle, early life-history processes (dispersal, energetics and survival) and prey production were simulated under incrementally perturbed flow (from –10 to –30%) and temperature (+1 and +2°C) regimes over 50 years. Simulated flow reduction and warming synergistically contracted spring spawning habitats (by up to 51%) and periods (by 19%). Under these conditions, fewer mature females entered a reproductive cycle, and more females skipped spawning, reducing spawning biomass by 20–50%. Many spawners migrated further to avoid increasingly unfavourable habitats, intensifying local density dependence in larval stages and, in turn, increasing size-dependent predation mortality. Diminished egg production (by 20–97%) and weakened recruitment pulses (by 46–95%) ultimately reduced population size by 21–74%. These simulations illustrate that environmentally amplified maternal influences on early life histories can lower sturgeon population stability and resilience to ever-increasing perturbations.