TITLE PAGE - acumen - The University of Alabama
TITLE PAGE - acumen - The University of Alabama TITLE PAGE - acumen - The University of Alabama
Crayfish sampling Sampling for crayfish began in November 2005 in Hering, January 2006 in Limrock, and July 2006 in Tony Sinks caves and was conducted semi-monthly (conditions permitting) until August 2011. On each visit, study reaches were visually surveyed by two observers on foot and all crayfish encountered were collected using dip-nets. Captured crayfish were marked using both internal tags [Visible Implant Alpha Tags (VIAT), Northwest Marine Technology, Shaw Island, WA, USA] and Visible Implant Elastomer (VIE; Northwest Marine Technology). VIATs are small (1.0 × 2.5 mm), fluorescent, uniquely numbered tags that were placed beneath the abdominal cuticle. The VIE was injected directly posterior to the VIATs and was used to assess tag loss, which was infrequent. Once marked, the ocular carapace length (OCL; posterior margin of ocular cavity to posterior center-margin of carapace) of each crayfish was measured (±0.1 mm) with dial calipers and was then released near the point of capture. OCL was used rather than TCL to avoid errors due to damage to the acumen following release (Venarsky et al., 2012b). Growth Annual crayfish growth rates (G) were estimated as: where W fn is g AFDM upon recapture, W in is g AFDM at initial marking, and yr is years elapsed. Length-AFDM equations for O. australis were acquired from Huntsman et al. (2011a). Since growth increments are “episodic” due to the molting cycle, annual growth increments were only calculated for individuals recaptured over intervals of 350 days or longer to ensure that molting occurred between recapture events. Negative annual growth-increments were attributed to measuring error and were excluded from analyses. For crayfish recaptured multiple times, the annual growth increment was calculated using the recapture date closest to the 350-day 105
minimum (Venarsky et al., 2012b). Annual growth increments were regressed against average crayfish biomass (g AFDM) to estimate the size-specific annual growth rate. Abundance and biomass The abundance and biomass of O. australis in each cave was estimated from June 2007 to May 2011 (~46 months or 3.8 years) with sampling occurring at monthly or bimonthly intervals. Crayfish abundance was estimated using the mark-recapture data (described in “Growth” section above) and Program MARK (White & Burnham, 1999). A “Closed Capture” model in Program MARK was used, which assumes that no births, deaths, immigration or emigration occurs. Because the data set spanned multiple years, some assumptions were probably violated. However, the severity of these violations were likely minimized because: i) O. australis is longlived (≤ 22 years; Venarsky et al., 2012b) suggesting low mortality rates, ii) only 8 ovigerous females were found among the 3 caves, indicating recruitment was minimal, and iii) sizefrequency histograms were not significantly different among years within each cave, suggesting a stable population structure (see Crayfish production section in Results). The most severe violations were likely those regarding immigration and emigration. However, immigration and emigration were likely minimal within the greater groundwater recharge area (e.g. analogous to surface stream watersheds) of the caves. Each model produced during the Program MARK analysis was ranked based on Akaike’s information criterion (AIC); the lowest AIC value represents the best fit model for the data (Akaike, 1973; Burnham & Anderson, 2002). Crayfish abundance was converted to biomass by first distributing the total population size acquired from Program MARK among the observed size-classes in a cumulative sizefrequency distribution of carapace lengths for each cave. Biomass was then calculated using the geometric mean of each size-class. Estimates of abundance and biomass were standardized to 106
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minimum (Venarsky et al., 2012b). Annual growth increments were regressed against average<br />
crayfish biomass (g AFDM) to estimate the size-specific annual growth rate.<br />
Abundance and biomass<br />
<strong>The</strong> abundance and biomass <strong>of</strong> O. australis in each cave was estimated from June 2007 to<br />
May 2011 (~46 months or 3.8 years) with sampling occurring at monthly or bimonthly intervals.<br />
Crayfish abundance was estimated using the mark-recapture data (described in “Growth” section<br />
above) and Program MARK (White & Burnham, 1999). A “Closed Capture” model in Program<br />
MARK was used, which assumes that no births, deaths, immigration or emigration occurs.<br />
Because the data set spanned multiple years, some assumptions were probably violated.<br />
However, the severity <strong>of</strong> these violations were likely minimized because: i) O. australis is longlived<br />
(≤ 22 years; Venarsky et al., 2012b) suggesting low mortality rates, ii) only 8 ovigerous<br />
females were found among the 3 caves, indicating recruitment was minimal, and iii) sizefrequency<br />
histograms were not significantly different among years within each cave, suggesting<br />
a stable population structure (see Crayfish production section in Results). <strong>The</strong> most severe<br />
violations were likely those regarding immigration and emigration. However, immigration and<br />
emigration were likely minimal within the greater groundwater recharge area (e.g. analogous to<br />
surface stream watersheds) <strong>of</strong> the caves. Each model produced during the Program MARK<br />
analysis was ranked based on Akaike’s information criterion (AIC); the lowest AIC value<br />
represents the best fit model for the data (Akaike, 1973; Burnham & Anderson, 2002).<br />
Crayfish abundance was converted to biomass by first distributing the total population<br />
size acquired from Program MARK among the observed size-classes in a cumulative sizefrequency<br />
distribution <strong>of</strong> carapace lengths for each cave. Biomass was then calculated using the<br />
geometric mean <strong>of</strong> each size-class. Estimates <strong>of</strong> abundance and biomass were standardized to<br />
106
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