Little is known about the habitat preferences and needs of pallid sturgeon Scaphirhynchus albus, which was federally listed as endangered in 1990. To learn more about habitat use and selection by pallid sturgeon, sonic transmitters were surgically implanted in 27 individuals from the middle Mississippi River. Study fish were located 184 times (1–23 times/individual) from November 1995 to December 1999. Of the seven macrohabitats identified, pallid sturgeon were found most often in main‐channel habitats (39% of all relocations) and main‐channel border habitats (26%); the between‐wing‐dam habitats were used less often (14%). Strauss's linear selectivity index (Li) values indicated that study fish exhibited positive selection for the main‐channel border, downstream island tips, between‐wing‐dam, and wing‐dam‐tip habitats; they showed negative selection for main‐channel, downstream of wing dams, and upstream of wing dam habitats. Comparison of Li values for four temperature ranges and three daily mean discharge ranges revealed little change in habitat selection due to temperature or discharge. Habitat use patterns also were similar across seasons and discharge regimes, except during spring months when between‐wing‐dam habitats saw greater use and main‐channel and main‐channel border habitat use declined. These changes may have been a response to high river stages associated with spring flooding, which may create favorable feeding areas in the between‐wing‐dam habitats. Enhancement and restoration of habitat diversity, particularly downstream island tip and between‐wing‐dam habitats, may be necessary for the recovery of pallid sturgeon in the middle Mississippi River.
Accurate age information is critical to the biological understanding and management of most fish species, but particularly for species of concern, such as the pallid sturgeon Scaphirhynchus albus. The accuracy and precision of pallid sturgeon age estimates from pectoral fin ray sections has never been established, yet all accumulated age information for the species was collected using this technique. To examine the accuracy and precision of age estimates, 16 pectoral fin ray samples from age‐6 pallid sturgeon were obtained from Gavins Point National Fish Hatchery, South Dakota. The fin rays were sectioned, mounted, and independently examined twice by each of two readers. Only 28.1% of the age estimates accurately reflected the known age of the fish. Multiple readings of the same sample by the same reader (within‐reader precision) only agreed 25% of the time, differences being as great as 5 years between the two estimates. Between‐reader agreement was 46.9%, the two readers' estimates of the same fish differing by as much as 2 years. Because of low accuracy and precision, estimated ages from pallid sturgeon pectoral fin rays should be viewed with caution.
Wehrspann and Zorinsky reservoirs are located near the largest population center of Nebraska, which has contributed to high fishing pressure and overharvesting of resident populations of black crappie Pomoxis nigromaculatus and white crappie P. annularis. To protect these popular fisheries and increase angler catch rates, a 254‐mm minimum length limit was established on both reservoirs in 1994. Fall trap‐net catch rates of black crappies increased 535% in Wehrspann Reservoir (1994–1998) and 721% in Zorinsky Reservoir (1993–1998). Angler catch rates from 1994 to 1998 increased from 0.26 to 2.55 crappies/h in Wehrspann Reservoir and from 0.13 to 0.82 crappies/h in Zorinsky Reservoir. Harvest rates declined below 0.03 crappies/h in both reservoirs. Growth rates declined, age structure increased, and annual mortality remained high in both reservoirs after the limit was implemented. The length limit was successful at protecting the populations and increasing angler catch rates; however, a shift in size structure was not observed and few fish of harvestable size were collected. In response to the lack of fish over 254 mm and anglers' desire to harvest fish, evaluation of the 254‐mm regulations has led to an annual open season (i.e., lifting of the length limit) to provide some harvest while protecting the high angler catch rates and population densities of the stockpiled population.
Recreational fisheries are traditionally managed at local scales, but more effective management could be achieved using a cross‐scale approach. To do this, we must first understand how local processes scale up to influence landscape patterns between anglers and resources. We highlight how population‐based synchrony methods, used in conjunction with a complex‐adaptive‐systems framework, can reveal emergent spatial properties within social‐ecological systems such as recreational fisheries. Herein, we quantified the level of spatial synchrony in angler behaviour, defined the relationship between angler synchrony and distance among waterbodies, and highlighted social‐ecological attributes contributing to these patterns. We leveraged a 111 waterbody‐year (34 waterbodies, 5‐year collection period) recreational fisheries dataset from Nebraska, USA to address these objectives. Intra‐annual patterns in angler behaviour were moderately synchronous across large spatial scales and predominately unrelated to distance among waterbodies. Large‐scale synchronous patterns in angler behaviour emerged from local‐scale interactions between angler heterogeneity and waterbody diversity. Spatial synchrony in angler behaviour is an emergent property that resulted from local‐level processes that scaled up to form large‐scale patterns. We posit that angler utility in combination with waterbodies sharing these desired utility components caused spatial synchrony among anglers with similar preferences or specializations. The level of spatial synchrony in angler behaviour will therefore depend on the degree of angler heterogeneity and waterbody diversity on the landscape, with high or low levels of both leading to low and high levels of spatial synchrony respectively. Synthesis and applications. Synchrony‐based methods proved useful for unveiling an emergent property in recreational fisheries that is beneficial for effective cross‐scale management. It may not be appropriate to extrapolate information and apply uniform management actions among local waterbodies because angler behaviour was not synchronous at small scales. Rather, anglers respond uniquely to waterbody diversity and therefore substitute waterbodies may be dispersed throughout the landscape. Creating boat access, for example could yield unintended consequences for a particular angler group and cause local and regional shifts in angler behaviour. Evaluating appropriate management options will require a cross‐scale monitoring approach that captures angler heterogeneity and waterbody diversity at multiple scales.
Most fishery regulations aim to control angler harvest. Yet, we lack a basic understanding of what actually determines the angler’s decision to harvest or release fish caught. We used XGBoost, a machine learning algorithm, to develop a predictive angler harvest–release model by taking advantage of an extensive recreational fishery data set (24 water bodies, 9 years, and 193 523 fish). We were able to successfully predict the harvest–release outcome for 99% of fish caught in the training data set and 96% of fish caught in the test data set. Unsuccessful predictions were mostly attributed to predicting harvest of fish that were released. Fish length was the most essential feature examined for predicting angler harvest. Other important predictive harvest–release features included the number of individuals of the same species caught, geographic location of an angler’s residence, distance traveled, and time spent fishing. The XGBoost algorithm was able to effectively predict the harvest–release decision and revealed hidden and intricate relationships that are often unaccounted for with classical analysis techniques. Exposing and accounting for these angler–fish intricacies is critical for fisheries conservation and management.
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