Cold Snaps and Warm Winters are Bad News for Some Bay Creatures

 

Last week Kari discussed the concept of cold snaps in the Chesapeake Region and their potential impact on migratory animals that make the Bay their home in the summer and fall. This post will examine cold snaps and why they are so potentially detrimental to some of the Bay’s creatures.

First, let’s clear up a potential misconception; cold snaps, when temperature drops suddenly for days or weeks, are not a new phenomena in the Chesapeake. However, what is new is the phenomena of longer growing seasons the region has been experiencing over the last several decades. Longer growing seasons generally mean that winters start later and temperatures tend to stay warmer longer. Many animals that call the Bay home in Summer and Fall use the gradually cooling temperatures that normally occur in Fall as a cue to begin their southerly migration to warmer conditions. Now that the onset of winter is becoming increasingly delayed, these animals are missing their cue to migrate. And then when temperatures suddenly do drop to normal wintertime temperatures for the Chesapeake region, these animals are not equipped to handle it.

This past December, most of the US experienced warmer than normal temperatures. According to NOAA’s National Centers for Environmental Information, over 5200 daily record highs were tied or broken across the US during the month of December. To be clear, while the general trend has been for later and warmer winters, it is likely that the primary reason this past December was so warm is due to the influence of El Nino. Unfortunately, this was bad news for sea turtles along the Atlantic coast who, because of the warmer water temperatures, failed to head south in the fall like they do normally. During the first week of January, temperatures suddenly dropped to levels that are normal for this time of year and the turtles found themselves experiencing temperatures that they don’t have a natural ability to deal with. When an animal is incapacitated by a sudden plunge in temperature it is said to be cold-shocked or cold-stunned. Much like a person with hypothermia, a cold shocked animal can not function normally and can die if not moved to warmer conditions.

TURTLES4Over the past couple weeks, sea turtles from New England to North Carolina were caught off guard by the sudden plunge from temperatures that were unseasonably warm to temperatures that are cold, but not necessarily unusual  for this time of year. Because of this, about 500 sea turtles from New England and 800 from North Carolina had to be rescued and transported to warmer waters down south. Many of these were the highly endangered Kemp’s ridly turtles. Surprisingly, only two turtles have had to be rescued in Virginia.

As Kari alluded to in her post last week, this issue is not restricted to just sea turtles. Over the last few years, a number of migratory species have been caught off guard by sudden drops in temperature in the Bay region. In February of 2014, thousands of Speckled Trout died in the Rappahannock River and Tributaries of Mobjack Bay. speckSpeckled trout normally migrate to warmer waters down south during the Fall and Winter. However, milder winters over the past few years had enticed a large portion of the Trout population to over-winter in the Bay. February of 2014 was unusually cold and thousands of these trout ended up cold-shocked and they subsequently died.

In January of 2011, a cold snap killed about 2 million juvenile spot in Chesapeake Bay. Chesapeake Spot are generally spawned in March and spend most of their first year growing in tspothe tributaries of Chesapeake Bay. They leave the Bay in late Fall to spend the winter in
warmer coastal waters down south. Most are gone by December. These juveniles may have missed their cue to head south by a late start to winter.

Kari’s analyses suggest that the onset of winter is becoming increasingly delayed. While many people may be happy about

Figure 5: A simple stress model to show when warm autumns occurred.

A simple stress model to show when warm autumns occurred.

warmer temperatures later in the year, as we can see from the examples discussed above, this has the potential to wreak havoc with the migratory species that live in Chesapeake Bay. Could winters continue to warm to the point where species that currently migrate south in the winter start staying here all year? If our winters continue to warm, this may be a possibility for animals like Speckled Trout, Spot, and sea turtles since they seem perfectly happy to hang around as long as the water stays warm. This could potentially have negative impacts as they compete for habitat and food resources with the normal winter residents of Chesapeake Bay.

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