The Decline of the Winter Flounder.

Edited by Autumn Berlied

Over the last few decades, the abundance and distribution of some marine species have shown to be impacted directly by fishing and environmental factors. Mortality, as a result of environmental factors is greatest during the developing stages of larval and juveniles (1). Climate has shown a considerable amount of variation over time which has had effects on fish stocks and species abundance overall. Fish stocks are a term utilized by fisheries, referring to the population or total mass of isolated groups of certain species of fish. These isolated subpopulations continue to be at high risk of decline. Another possible factor that has been considered a potential external driver of the decline of certain species populations is the presence of over-fishing throughout the east coast.  

Figure 1: A winter flounder.

The Winter Flounder (Psuedopleuronectes americanus) is a cold-water species that is considered an important fish stock within the fishing industry. This species of flatfish inhabits estuaries where they migrate too and spawn in late winter/early spring (1). Water temperature within these estuaries is proven to be vital in success of winter flounder as it defines the habitat area suitable for the early developmental stages. Winter Flounders fit into a subcategory of Poikilotherms, organisms whose biologic processes (metabolism, growth, fecundity, etc.) are highly environmentally sensitive traits. Warming water temperatures, poor water quality from  

land run off, and harmful algal blooms have shown to affect survival (3). Although, this cold-water species holds an advantage over competitors as the low temperatures offer the developing eggs and larvae a “thermal refugee” from predation due to few predators residing in estuaries during winter (1).  

Figure 2: Stages of growth in winter flounder.

Generally, water temperatures have been warming for over three decades, posing a threat to the abundance of the Winter Flounder populations. Specifically, southern stock has seen a considerable decline and retreated north in the last few decades as water temperatures increase. These warmer water temperatures in the winter and earlier warming in the spring may allow predators to migrate to the estuaries much sooner, decreasing the positive impact of the thermal refugee (1).  

Figure 3: Impact of mean temperature over a span of months on density of biomass.

This cold-water species has seen decline in the last few decades related to overfishing and climate change despite the employment of restrictions. Further bringing the question; what is the major potential external driver for this species population decline throughout the US? Through analyzing stock productivity fisheries can work to preserve these fished species and benefit Winter flounder management.  

Figure 4: The American Fisheries Society has worked over the last few decades to identify species that were at high risk of extinction. They established a productivity index that identifies categories of risk based on parameters including intrinsic rate of increase, fecundity, age at maturity, etc.  

Many economically essential fish are on the decline mainly due to overharvesting and climate change. Along the east coast, the Winter Flounder specifically has seen significant effects from overfishing and environmental changes. Species management is crucial to maintain the well-being of these fish stocks. 

Sources: 

Bell, R. and Hare, J. ‘Externally Driven Changes in the Abundance of Summer and Winter Flounder”. Journal of Marine Science. 71(9), 2416-2428. (2014). 

Latour, R. and Gartland, J. “The Trophic Dynamics of Summer Flounder (Paralichthys Dentatus) in Chesapeake Bay”. Fishery Bulletin. Vol 106, (1), 47-57. (2008)  

Sagarese, S., and Frisk, M. “Movement Patterns and Residence of Adult Winter Flounder within a Long Island Estuary”. Dynamics, Management, and Ecosystem Science. Vol 3 (1).  

Schwieterman, G., and Crear, D., et al. “Combined Effecrs of Acute Temperature Change and Elevated pCO2 on the Metabolic Rates and Hypoxia Tolerance of Clearnose Skate, Summer Flounder, and Thorny Skate”. Fish Metabolic Physiology in Response to Stress. 8(3), 56. July 2019.