Brian S. Dorr

Size Selectivity of Crappie Angling

Abstract Over 6,000 black crappies Pomoxis nigromaculatus and white crappies P. annularis were tagged in five lakes and reservoirs to quantify size selectivity of angling. Total length of fish tagged ranged from 20.0 to 39.8 cm; fish caught by anglers ranged from 20.0 to 38.8 cm. Return rates were low at lengths near 20 cm, increased gradually to a peak between 26 and 32 cm, and decreased for longer fish. This pattern was consistent among the five lakes and reservoirs and did not differ between species. Observed size-selective exploitation resulted in the lopsided removal of intermediate age-classes, thereby simulating a reversed slot length limit. Crappie population dynamics and fisheries can be severely affected if angling selectivity and exploitation are high. Management of crappies to favor desirable population characteristics may need to focus on enhancing or weakening the effect of size selectivity.

Habitat associations of gopher tortoise burrows on industrial timberlands

Abstract The western population of the gopher tortoise (Gopherus polyphemus) was listed as threatened under the Endangered Species Act in 1987 due to extensive population declines. Declines have been linked to site conversion of native pine (Pinus spp.) forests for urban development, agriculture, and commercial forest management. We conducted surveys to detect tortoise burrows on corporate timberlands in southern Mississippi and southwestern Alabama during summer 1994. We surveyed 2,759 0.5-ha strip transects on soil types of 9 different suitability categories for gopher tortoises. We found 460 active and 264 abandoned burrows on the 1,380 ha surveyed. Edaphic and vegetative conditions, such as sandy soils and total and midstory canopy coverage, influenced gopher tortoise occurrence. Logistic regression analyses revealed that active burrow occurrence was related positively to deep, sandy soils and related negatively to total canopy closure and fine loam soils with limited sand content. Abandoned burrow occurrence was related positively to increasing midstory canopy closure and selected soil types. Sandy soils and open over-story canopy that created favorable burrowing, nesting, and foraging conditions were important influences in active burrow occurrence. Vegetation management techniques, such as prescribed fire, midstory control, and intermediate forest stand thinning, are recommended on gopher tortoise conservation areas and connective corridor habitats on commercial timberlands. We theorize that restoration of longleaf pine (P. palustris) forests on sandy ridges can produce desirable core habitats and dispersal corridors for gopher tortoises in landscapes dominated by intensively managed pine plantations.

Management effects on breeding and foraging numbers and movements of double-crested cormorants in the Les Cheneaux Islands, Lake Huron, Michigan

ABSTRACT The yellow perch fishery of the Les Cheneaux Islands (LCI) region of Lake Huron, MI suffered a collapse in 2000, attributed in part to the increase of double-crested cormorants (Phalacrocorax auritus) in the region. A management program involving egg-oiling and lethal culling was initiated in 2004 to reduce cormorant foraging on yellow perch in the LCI. Counts of cormorant nests, nests oiled, cormorants culled, and aerial counts and telemetry surveys were used to evaluate management. Management contributed to a 74% reduction of cormorants on breeding colonies from 2004 to 2007. Cormorants used the LCI area significantly more (P<0.05) than surrounding areas. Aerial counts of foraging cormorants declined significantly (P<0.05) over the entire survey area but not within the LCI proper. However, aerial counts of cormorants in the LCI were five-fold less than cormorant counts in the same area in 1995. Reduced cormorant numbers were attributed in part to the elimination of cormorant nesting on a large colony due to the introduction of raccoons. Although the numbers of cormorants using the LCI did not decline, flocks were significantly smaller and more dispersed after management began. The reduced number of cormorants from 1995 levels and more dispersed foraging likely reduced predation on fish stocks including yellow perch in the LCI. Our findings indicate that the relationship between reduction in cormorant breeding numbers and reduced cormorant foraging in a given area is complex and may be influenced by density dependent factors such as intraspecific competition and quality of the forage base.

Effect of Roost Harassment on Cormorant Movements and Roosting in the Delta Region of Mississippi

Abstract Double-crested Cormorant (Phalacrocorax auritus) predation on Channel Catfish (Ictalurus punctatus) at commercial farms has been estimated to cost the Mississippi aquaculture industry approximately

Foraging ecology and depredation management of great blue herons at Mississippi catfish farms

5 million annually to replace consumed fingerlings. In 1997, catfish producers assumed responsibility for the dispersal of cormorants in night roosts in the eastern (interior) delta region of Mississippi, where catfish farms are concentrated. We documented movements of 50 cormorants marked with radio transmitters in the delta region from January through March 1997. We obtained 161 post-capture day locations and 176 post-capture night roost locations. Cormorants that were harassed at their night roost flew farther to their next day’s location than birds that were not harassed the previous night. Of the cormorants for which we had more than one night roost location, only 11% of cormorants that were harassed returned to the same roost within 48 hours, compared with an 81% return of cormorants to a previously un-harassed night roost. Moreover, cormorants in the eastern portion of the delta (where all harassment was conducted) changed night roosts more frequently than cormorants in the western (non-harassed) delta. Since cormorants in our study foraged relatively close to their night roosts and only 11% of the birds that we observed roosting in the western delta traveled to the eastern delta to forage the following day, coordinated and intensive dispersal of cormorants from the interior delta may, temporarily, limit cormorant impacts to Mississippi aquaculture.

Double-crested Cormorant Movements in Relation to Aquaculture in Eastern Mississippi and Western Alabama

Great blue herons (Ardea herodias) occur at high densities at catfish farms in the southern United States. They are perceived by farmers to prey heavily on fish stocks. After a field study at selected catfish farms in Mississippi, we describe (1) the pond conditions where great blue herons intensively foraged, (2) the prevalence of disease in catfish that were captured by herons, and (3) predation rates and economic effects of herons among selected pond situations. Heron abundance was significantly associated with season and was greatest during the fall (Sep-Oct). We characterized catfish ponds as having high (≥6 birds) or low (≤3 birds) foraging activity by herons and characterized pond type, disease prevalence, and water quality. Categorical models showed a significant association of heron activity with disease prevalence in ponds (diseased) and fingerling ponds. Based on model parameters and associated odds ratios, high heron activity was 6.6 times greater at fingerling ponds than at food-fish ponds, and 40.1 times greater at diseased ponds than at those without diseased fish. This was presumably because fingerlings are a more desirable prey size, and disease makes catfish more vulnerable to heron predation. Based on pathology reports, 85% (n = 55) of the live catfish captured by herons from high-activity ponds were diseased, of which 76% were considered to have a terminal condition. In contrast, 75% (n = 63) of the catfish captured by herons congregated at ponds where catfish were being fed were diagnosed as healthy and only 3 (5%) were considered to have a terminal condition. Although both disease and fish feeding bring catfish to the surface and increase their vulnerability to heron predation, we suggest that heron harassment efforts by farmers be focused during fish feeding when heron capture rates are the highest and the greatest predation on healthy catfish occurs. Based on heron foraging rates, average numbers of herons seen, and the duration of foraging activity, we estimated low expected heron predation losses at catfish ponds over time. Assuming that predation losses observed in this study are representative, we conclude that catfish predation losses from great blue herons are either insignificant or readily preventable.

A Socioeconomic and Biological Evaluation of Current and Hypothetical Crappie Regulations in Sardis Lake, Mississippi: An Integrated Approach

Abstract Concomitant with increasing numbers of the Double-crested Cormorant (Phalacrocorax auritus), catfish producers in eastern Mississippi and western Alabama have reported damage caused by cormorant predation. VHF telemetry was used to document movements of 25 cormorants from all known night roosts in the aquaculture producing areas of eastern Mississippi and western Alabama, January-April 1998. A total of 193 day locations and 396 night roost locations of the cormorants were obtained. Each cormorant was found in the study area for 57 ± 4 (SE) days. Each cormorant averaged three night roosts (range: 1-8) and spent 20 (±2) days at each night roost site. Over 95% of cormorant day locations were within 19 km of their night roosts. Catfish pond use by cormorants varied between roost sites. Cormorants from five of eleven night roosts had ≥30% of subsequent daytime locations on catfish ponds and birds from five of the six remaining night roosts did not visit catfish ponds on the following day. Foraging distance and frequency of night roost interchange was less for birds in this study than those reported from other aquaculture regions. We suggest roost harassment efforts should be focused on specific roost sites and some roost sites should serve as unharrassed refugia from which cormorants are less likely to cause damage to aquaculture.

Weathered MC252 crude oil-induced anemia and abnormal erythroid morphology in double-crested cormorants (Phalacrocorax auritus) with light microscopic and ultrastructural description of Heinz bodies

Abstract We conducted a socioeconomic survey and review of existing biological data in an integrated evaluation of current and hypothetical fishery regulations on crappies Pomoxis spp. in Sardis Lake, Mississippi. The objectives of this study were to (1) assess angler acceptance of current and hypothetical harvest restrictions, (2) determine the recreational value of the crappie fishery to its participants, (3) estimate possible changes in recreational value based on angler responses to hypothetical regulations, and (4) integrate the results of the socioeconomic surveys with existing biological information. Using the travel cost method, we estimated mean expenditures at US

Development of methods for avian oil toxicity studies using the double crested cormorant (Phalacrocorax auritus)

29.48 and average consumer surplus per angler per trip at

Changes in white cell estimates and plasma chemistry measurements following oral or external dosing of double-crested cormorants, Phalacocorax auritus , with artificially weathered MC252 oil

8.88. We estimated 75,601 crappie angler trips in 1995, yielding an annual consumer surplus for the Sardis Lake crappie fishery of