We examined the role of harvest in the collapse of the population of yellow perch Perca flavescens in southwestern Lake Michigan during the mid to late 1990s. After the great decrease in this population at that time, commercial fisheries in Illinois and Wisconsin were closed during 1996-1997 (and have remained closed), and stricter regulations were placed on recreational fisheries. Reproductive failure has been implicated as the primary cause of the population collapse, but the role of fishing in the collapse was not rigorously investigated in previous studies. We conducted an age-, size-, and sex-structured stock assessment of yellow perch to estimate population size and examine historical trends in fishing mortality in Illinois and Wisconsin waters of southwestern Lake Michigan. Model estimates indicated that yellow perch abundance in 2002 was less than 10% of the 1986 abundance in Wisconsin and about 20% of the respective population in Illinois. Annual mortality rates for females age 4 and older averaged 69% during 1986-1996 in Wisconsin and 60% in Illinois during 1986-1997, rates that are quite high for a species like yellow perch, which can live longer than 10 years. The estimated fishing mortality rates of adult females during 1986-1996 exceeded widely used reference points, suggesting that overfishing may have occurred. Fishing mortality rates decreased substantially in the late 1990s after stricter regulations were imposed on recreational fisheries and commercial fisheries were closed. We believe that unsustainably high mortality rates from fishing were a substantial contributing cause of the rapid decline of mature females in the mid-1990s. Spawning stock biomass in 2002 was at its highest level since the early 1990s despite relatively poor recruitment during the past decade. In part, this development reflects the fact that management actions have successfully reduced fishing mortality.

SynopsisEcomorphological correlates were sought among ten species of distantly related subtropical seagrass fishes . Morphomet ric data associated with feeding and microhabitat utilization were compared by principal components analysis, cluster analysis, and canonical correspondence analysis to dietary data . Morphology was generally a poor predictor of diet except for a group of mid-water planktotrophic filter feeders . Separation of the species along morphological axes appears to be related more to microhabitat utilization resulting in three major groups: (1) a group of planktotrophic, mid-water fishes specialized for cruising and seeking out evasive prey characterized by a compressed fusiform body, forked caudal fin, long, closely spaced gill rakers, short to intermediate length pectoral fin, pointed pectoral fin, large lateral eye, short head, and a terminal or subterminal mouth ; ( ) slow swimming, less maneuverable epibenthic fishes that pick or suck their prey off the substrate . They are united by more rounded caudal and pectoral fins, and short or no gill rakers ; and ( ) a group of more mobile and maneuverable epibenthic foragers characterized by a more compressed, sub-gibbose body, long, pointed pectoral fins, forked caudal fins, large lateral eyes, subterminal mouth, and greater jaw protrusibility. Cases of convergence in trophic and microhabitat utilization characters were apparent in some of the groups .

SynopsisOntogenetic dietary shifts are well studied in fishes. However, these shifts are rarely correlated with habitat and morphology. This study investigates: (1) ontogenetic dietary changes in mullet; and if dietary shifts do occur (2) whether they are correlated with feeding location, feeding behavior andlor feeding morphology. Stomach contents from eight size classes, each with 25 individuals, were analyzed using a gravimetric sieve fractionation procedure, Czechanowski's Quantitative Index and cluster analysis. Core samples (5 mm deep) were also analyzed in the same manner. Morphological characters were measured to detect differences among the size classes. Cluster analysis showed three distinct trophic units for Mugil cephalus in Cross Bayou: (1) 20.0 mm standard length -30.0 mm SL; (2) 30.0 mm SL -40.0 mm SL; and (3) 40.0 mm SL -> 100 mm SL. Comparison of the gut contents to the sediment contents for each size class showed an increase in similarity as the fish grew. Mullet gut contents from fish 20-25 mm SL were only 45% similar based on the weights of the prey items to the sediment subsample prey items, while stomach contents from fish > 100 mm SL were 84% similar to the sediment subsample contents. Gill raker length and interraker spacing of four gill arches were allometric with respect to standard length. Prey particle size within size classes appeared to be more correlated with feeding behavior than gill interraker spacing because smaller particles than predicted by the interraker spacing were ingested. It is suggested that smaller fish may be browsing more selectively than larger fish which graze.

To assess potential effects of climate change on Great Lakes fish populations, we evaluated trends in the reproductive phenology of Yellow Perch Perca flavescens (spring spawner) and Lake Trout Salvelinus namaycush (autumn spawner). For Yellow Perch in Lake Michigan, the estimated reproductive midpoint date (50% of mature females ripe or spent, 50% not yet spawned) took place 6.2 d/decade earlier in the spring near Milwaukee from 1988 to 2012 and 1.8 d/decade earlier in Green Bay from 1980 to 2012. At both locations water temperatures at the spawning sites on the midpoint date showed no trends, but mean water temperatures during the spring at the spawning site and midlake increased over the study period. This suggests that Yellow Perch spawning areas were warming sooner in the spring and that Yellow Perch were spawning earlier to maintain a consistent spawning temperature. Lake Trout phenological patterns were more complex. For Lake Trout in Lake Michigan near Milwaukee, there was a marginally significant trend for spawning to take place 2.1 d/decade later in the autumn from 1983 to 2006. However, water temperatures at the spawning site at the midpoint date did not change and autumn temperatures at the site and at midlake did not show a warming trend. For Lake Trout in Lake Superior near the Apostle Islands, the midpoint date did not change from 1988 to 2012. Water temperatures at the spawning site on the midpoint date and during the autumn also showed no trends, but midlake summer and autumn water temperatures increased significantly. Overall, Yellow Perch in Lake Michigan have shifted reproductive timing in a manner consistent with a warming climate, but the relationship of climate change to reproductive phenology remains unclear for Lake Trout in Lake Michigan and Lake Superior.The earth's climate is warming, resulting in major changes in the thermal conditions of many lakes (Magnuson et al. 2000;Schneider and Hook 2010). Over the last century, the Laurentian Great Lakes have experienced well-documented trends towards less ice and shorter winters (Assel and Robertson 1995;Assel et al. 2003), warmer summer temperatures

Two marking techniques, fin removal and visible implant elastomer, were evaluated in walleye Sander vitreus. Although fin‐clipping is widely practiced, research results have been ambiguous as to whether the technique is harmful to fish over the long term. We attempted to determine over a 7‐year period whether elastomer marking might have significant benefits to growth and survival of walleye when compared with fish given a single fin clip. We also evaluated the long‐term detection rates of elastomer marks as well as their cost‐effectiveness. Each year for 5 years we marked and stocked an average of 8,000 extended‐growth walleye fingerlings in the lower Milwaukee River, Wisconsin, as part of a project to reintroduce walleyes to the Milwaukee River estuary. One‐half were given a single fin clip and one‐half were given an elastomer mark. Fin clips and elastomer colors were changed each year. Fish were recaptured the following year by means of electrofishing gear. We found no significant differences in survival or growth rates between the differentially marked fish. We also found that tag detection in recaptured fish over the long term was 82.5% for fish originally marked with elastomer. The cost associated with elastomer marking was US$0.40 per mark while the cost of fin clipping was $0.03 per mark. We concluded that a single fin clip was the more desirable technique for marking walleyes.