Auburn University's
Mobile-Tensaw Delta Largemouth Bass Project Result Bullets
Here are some brief "bullets" from our first year of work (2002).
- We sampled the Delta on 15 dates during 2002, monthly during January through April and October through December, and twice per month during May through August.
- Water temperatures rose to 95 F in mid summer, and dropped to around 50 F over winter across all of the sites in the sampling area.
- While there was no measurable salinity at any time at any depth at the uppermost site (Dennis Lake), there was an obvious salt wedge that occurred in deeper waters for most of the summer at Gravine Island (an intermediate site), and salinity was equal throughout the water column below the causeway (e.g., D'Olive Bay).
- Salinity peaked at downstream sites during summer months. Peak salinity levels at D’Olive Bay, our most downstream site, were 7.9‰ in August.
- During the first year of the study, we collected a total of 1,346 young-of-year (YOY) largemouth bass.
- Swim-up dates for YOY largemouth bass collected in June occurred earliest downstream and latest upstream.
- YOY largemouth bass catch-per-effort (CPE) did not differ across sites from upstream to downstream.
- Growth of YOY largemouth bass was more rapid at D'Olive Bay, Bay Minette Basin, and Crab Creek, than at sites further upstream at Gravine Island, McReynold's Lake, and Dennis Lake.
- Mean daily growth rates of YOY largemouth bass were greater at D'Olive Bay, Bay Minette Basin, Crab Creek, and Gravine Island, than at McReynold's Lake and Dennis Lake.
- YOY largemouth bass diets included marine-derived shrimp, aquatic insects, fish, and amphipods as the most important prey items at each site.
- Catch rates followed a seasonal pattern with increased catch rates typically occurring in winter, spring, and fall months and decreased catch rates occurring during summer months. Sites (D’Olive Bay, Gravine Island, Dennis Lake) with lowest catch rates were also sites (Bay Minette, Crab Creek, McReynold’s Lake) most closely connected to or part of a main river channel, while sites with highest catch rates were also sites least connected to a main river channel.
- Mean sizes also followed a seasonal pattern with increased catch rates typically occurring in winter, spring, and fall months and decreased catch rates occurring during summer months.
- The largest bass collected was 6.2 lbs. from McReynold’s Lake. Only three bass = 5 lbs. were sampled, and all were from upstream sites.
- Few bass = age-4 were found both upstream and downstream.
- Survival was relatively low both downstream (50%) and upstream (41%).
- Significantly higher growth to age-1 was found at downstream sites relative to upstream sites.
- Relative weights (“fatness” of fish) were greater at downstream than upstream sites.
- Bass consumed a greater % biomass of invertebrates downstream relative to upstream. Blue crabs and white shrimp ranked highest in invertebrate biomass consumed by bass downstream. Hence, the largest % biomass was from marine- and estuarine-derived prey types in downstream bass diets and was greater than in upstream bass diets. Diets of upstream bass consisted of a greater biomass of fish and freshwater-derived prey types.
- External tagging of bass began in July 2002 and resulted in the tagging and release of 190 bass. Only one bass was recaptured in our sampling. Low numbers of tagged fish and recaptures were likely due to starting mid-year.
Click HERE to return to Auburn Univeristy's Mobile-Tensaw Largemouth Bass web page