Quantifying and Identifying Factors Influencing Length Changes in Popular Freshwater Fishes Preserved in Ice

Fish length data are important for assessing sportfish populations and establishing and enforcing length-based harvest regulations. Evidence suggests that fish length can change after preservation in ice. These changes can impact comparison of live-caught and post-catch length measurements and therefore angler compliance to regulations, a concern raised by state law enforcement personnel. Similarly, length changes may skew length-based analyses done by fisheries managers. We evaluated TL changes of largemouth bass (Micropterus salmoides), catfishes (Ictaluridae spp.), black crappie (Pomoxis nigromaculatus), and sunfishes (Lepomis spp.) collected in Florida and preserved in coolers of ice for intervals of 3–6 h, 24 h, and 36 h. Our re- sults indicate mean percent shrinkage ranged 0.43%–1.58% among time intervals and fish groups but significantly differed by group and time interval. We found measurement variability and ambient water temperature to be insignificant factors to observed length changes. Where length measurement accuracy is important, fisheries managers should be aware of potential shrinkage of fish post mortality, including during preservation in coolers of ice. As a general recommendation for law enforcement, we suggest absolute shrinkage allowances of 6 mm (0.25 inches) for black crappie and sunfishes and 13 mm (0.5 inches) for largemouth bass and catfishes, when assessing angler compliance to length-based fish regulations after preservation in coolers of ice.

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