Alligator distribution, size, and hole occupancy and crocodile juvenile growth and survival
July 2007 - March 2015
- Corps of Engineers
Responses of crocodilians are directly related to suitability of environmental conditions including hydropattern. Correlations between biological responses and environmental conditions contribute to understanding of species' status and trends over time. Positive or negative trends of this indicator relative to hydrologic changes permit assessment of positive or negative trends in restoration impacts. Restoration success or failure would be evaluated by comparing recent and future trends and status of crocodilian populations with historical population data and model predictions; as stated in the CERP hypotheses related to alligators and crocodiles (CERP MAP section 220.127.116.11 and 18.104.22.168, 2004). Importantly, these data can be used in an analysis designed to distinguish between effects of CERP and non-CERP events such as hurricanes or droughts. Data from this MAP project will be used to develop, refine, and validate spatially explicit crocodilian population models, which can then be applied in setting interim goals and targets. This project also fills a critical research need (refining crocodile/salinity relationship) identified as part of RECOVER recommendations for setting interim goals and targets. The objectives and work proposed here follow the recommendations from the MAP, Part 2: 2006 Assessment Strategy for the MAP and the RECOVER GE Trophic Sub-team, to enhance and build upon research and monitoring programs for alligators and crocodiles that have been funded as part of the CESI, Modified Water Deliveries, and RECOVER MAP. This work is designed to satisfy requirements for monitoring changes in alligator and crocodile populations over different time scales as a result of restoration. Generally, the statement of work (SOW) described below is intended to support four broad objectives of the MAP: 1. Establish pre-CERP reference state including variability for each of the performance measures; 2. Determine the status and trends in the performance measures; 3. Detect unexpected responses of the ecosystem to changes in stressors resulting from CERP activities; 4. Support scientific investigations designed to increase ecosystem understanding, cause-and-effect, and interpret unanticipated results. CERP and RECOVER MAP hypotheses and goals related to crocodilians Alligators � Expand distribution of reproducing alligators and alligator holes to southern marl prairies/rocky glades and restore the keystone role of alligator holes as refugia for aquatic fauna; � Provide salinity regimes that are suitable for expansion of reproducing alligators into oligohaline portions of estuaries; � Increase in current populations and body condition of reproducing alligators in ridge and slough landscape. Crocodiles � Restoration of freshwater flows to estuaries and salinity regimes will increase growth and survival of crocodiles. � Restoration of location of freshwater flow will result in an increase in relative density of crocodiles in areas of restored flow, such as Taylor Slough/C-111 drainage. Tasks Alligators 1. Finish developing and testing a monitoring program for relative distribution, size (condition), nesting and hole occupancy rates of the American alligator in response to CERP projects as specified in the MAP. The monitoring program and procedures developed will provide the baseline for future comparisons and an effective means for evaluating restoration success for the American alligator in the GE ecosystem. 2. Monitor changes in alligator populations due to restoration over short (body condition), medium (distribution, hole occupancy) and long (nesting) temporal and spatial scales. Crocodiles 1. Finish developing and testing a monitoring program for nesting, condition, growth and survival of crocodiles in areas that will be affected by CERP projects. 2. Monitor changes in nesting, condition, growth, and survival of crocodiles in response to CERP projects.