Seasonal Condition of Adult Striped Bass Relative to Thermal Habitat and Forage Availability

Adult striped bass (Morone saxitilis) are vulnerable to high summer water temperatures and low dissolved oxygen (DO) in southern reservoirs, potentially resulting in poor body condition and elevated mortality. In Lake Buchanan, Texas, mean relative weights for striped bass >500 mm ranged from 77 to 84 from 2002-2007 in spring surveys when relative weight should be maximized. Two hypotheses were tested that could explain the observed poor condition of Lake Buchanan adult striped bass in spring: (1) lack of available prey, or (2) lack of suitable habitat during the previous summer. Striped bass condition was monitored monthly from August 2007 to March 2008 and additionally in October 2008 and February 2009. Sampling of vertical and horizontal forage distributions was conducted concurrently from September 2007 to March 2008. Mean striped bass relative weights increased from 68 in August 2007 to 91 in March 2008, an increase of 0.12 Wr/d; in contrast, vertical and horizontal forage distributions in the reservoir did not vary seasonally. Additional sampling in October 2008 and February 2009 corroborated this seasonal trend in condition as mean relative weights were 74 and 81 respectively. Lake Buchanan experienced prolonged periods (>2 mo) during summer when no preferred thermal habitat existed for striped bass. Low spring condition of adult striped bass in Lake Buchanan was likely due to a hold-over effect of stress caused by a lack of preferred thermal habitat (i.e., temperature <25 C and dissolved oxygen >2 mg L-1) during the previous summer. For reservoirs with warmer summer temperatures or more extended warm water periods, maintaining quality striped bass fisheries may not be possible and management alternatives such as stocking the more temperature-tolerant hybrid striped bass may be preferable.

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