Habitat-specific Effects on Southern Flounder Growth and Sex Ratios in Mobile Bay

Habitat-specific Effects on Southern Flounder Growth and Sex Ratios in Mobile Bay Meghan Angelina

Southern flounder (Paralichthys lethostigma) are an economically important species that use a variety of habitats across salinity gradients along the Atlantic Ocean and the Gulf of Mexico. However, in recent years, their abundance and fishery harvests have declined throughout the species' range...

Growth

Exponential growth of newly settled Southern Flounder (Figure 6, Glass et. al, 2008)

It is crucial that fish identify habitats that promote their rapid growth, since they're vulnerable to predation and hydrological features of the ocean. Faster growth confers to survival advantages, and growth rates may vary with environmental conditions.

Source: The Fisheries Blog

Sex Ratios

Midway et. al, 2013

The fishery targets larger fish, so females represent the vast majority of the commercial and recreational catches.

Source: The Fisheries Blog

Temperature-dependent sex determination (TSD)~ If there are extreme temperatures existing in an area, juvenile females are able to reverse their sex and develop male phenotypic qualities when they are between 35 and 80 millimeters. It is energetically inexpensive to be a male because they are small and do not have to produce eggs.

An optimal temperature that promotes female growth was identified in a controlled laboratory setting (Figure 5, Luckenbach et. al, 2003). It is at this point when a 1:1 male to female ratio can be achieved. There will be a skew to male bias in any extreme situation.

Mobile Bay

Estuary along the Gulf of Mexico

4th largest freshwater discharge by volume, which creates a defined salinity gradient

Important nursery habitat

Historically has been known to support large harvests of Southern Flounder

Methods

Temperature HOBO loggers are housed within 2 layers of PVC, and they are collecting temperature data every 30 minutes. We are collaborating with organizations that have active salinity loggers close to our 11 stations.

A variety of gear types (otter trawl, beam trawl, gill net, seine net, boat electrofishing) will be used to collect juvenile and adult Southern Flounder in May, July, and September each year.

Otoliths are fishes' ear bones that can give us information about age, growth, and residency. After being sectioned, the rings on sagittal otoliths can be counted in just the same way you would count rings on a tree. They will be used to age and back-calculate growth rates.

Gonads will be used to quantify sex-specific biomarkers (i.e. cytochrome P450 Aromatase) to identify phenotypic sex, histologically.

Results

We expect results to highlight the potential of specific habitats to produce recruits to the fishery by driving significantly different growth rates and sex ratios

Conclusions and Significance

Little is known about the consequences of Southern Flounders' varied habitat-use and the processes that drive their variable growth rates.

Female Southern Flounder face excessive pressure because they are harvested, while the ones that remain have the potential to reverse sex in extreme temperatures. Environmentally-relevant conditions impact sex ratios, and the potential for sex reversal impacts population dynamics.

Results of this study will support improved management of Southern Flounder in Alabama by identifying how critical habitats affect their physiological responses to environmental variations within the estuary.

Acknowledgements

Alabama Department of Conservation and Natural Resources~ Alabama Marine Resources Division

Dr. Troy Farmer (Principal Investigator), Jared Chrisp (Master’s student), and Mason Collins (Undergraduate technician)

Southern Flounder Diet and Distribution (Farmer Lab)

Coauthors: Lindsay Glass Campbell (U.S. Fish and Wildlife Service), Matthew Catalano (Auburn University), Eric Peatman (Auburn University)

References

Glass, L. A., J. R. Rooker, R. T. Kraus, and G. J. Holt. 2008. Distribution, condition, and growth of newly settled southern flounder (Paralichthys lethostigma) in the Galveston Bay Estuary, TX. Journal of Sea Research 59(4):259–268.

Glass Campbell, L. 2016, April 25. Nemo isn't the only transgender fish in the sea. web log.

Luckenbach, J. A., J. Godwin, H. V. Daniels, and R. J. Borski. 2003. Gonadal differentiation and effects of temperature on sex determination in southern flounder (Paralichthys lethostigma). Aquaculture 216(1-4):315–327.

Luckenbach, J. A., R. J. Borski, H. V. Daniels, and J. Godwin. 2009. Sex determination in flatfishes: Mechanisms and environmental influences. Seminars in Cell & Developmental Biology 20(3):256–263.

Midway, S. R., J. W. White, W. Roumillat, C. Batsavage, and F. S. Scharf. 2013. Improving macroscopic maturity determination in a pre-spawning flatfish through predictive modeling and whole mount methods. Fisheries Research 147:359–369.

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