Are there biases in biopsy sampling? Potential drivers of sex ratio in projectile biopsy samples from two small delphinids. Issue 4 (5th February 2013)

• Record Type: Journal Article
• Authors: Kellar, Nicholas M.; Trego, Marisa L.; Chivers, Susan J.; Archer, Fredrick I.; Minich, Jeremiah J.; Perryman, Wayne L.
• Is Part Of: Marine mammal science. Volume 29:Issue 4(2013)
• Page Start: E366
• Page End: E389
• Publication Date: 2013-02-05
• Subjects: Marine mammals -- Congresses; Marine mammals -- Periodicals; Marine mammals, Fossil -- Periodicals; Mammifères marins -- Périodiques; 599.5
• DOI: 10.1111/mms.12014
• Languages: English
• ISSNs: 0824-0469

Abstract

<abstract abstract-type="main" id="mms12014-abs-0001"> <title>Abstract</title> <p>Molecular assays were used to determine the sex of 1, 294 biopsied common dolphins (658 long‐beaked common dolphins, <italic>Delphinus capensis</italic>, and 636 short‐beaked common dolphins, <italic>D. delphis</italic>) in the Southern California Bight. Sex ratio differed substantially between the two species; females comprised 241 (36.6%) of <italic>D. capensis</italic> samples and 410 (64.5%) of <italic>D. delphis</italic> samples. All biopsies were taken either from a large research ship or from a small, rigid‐hull inflatable boat (RHIB) launched from the larger ship. When conducting replicate biopsy effort on the same schools from each vessel/platform ("Tandem Biopsy Sampling"), we found evidence that disproportionately more female <italic>D. capensis</italic> were biopsied from the RHIB than from the ship but the same was not true for <italic>D. delphis</italic>. We suspect that these results are driven by bowriding‐behavior differences between the two species. Biopsy duration, geographic location, school size, and Julian date were considered as potential covariates with sex ratio; geographic location was the only one to show strong evidence of correlation. This study also presents an alternative to the erroneous practice of comparing sex ratios to a theoretical assumption of parity (<italic>i.e</italic>., 50:50 sex ratio) when researchers avoid sampling animals paired with calves.</p> </abstract>