Peter C. Jacobson

Visions for Recreational Fishing Regulations

Abstract We review sportfishing regulations in Minnesota and across North America and discuss potential visions for the future of sportfishing regulations. Creel limits are ubiquitous across North America and they have been generally set arbitrarily with little biological justification. Anglers may not accept reductions in creel limits that actually decrease total harvest. Length-based regulations are now common and most North American sport fish management agencies had numerous water-specific length-based regulations. The future of fishing regulations could continue to get more complex but there are substantial shortcomings to this future. We present four visions of the future of freshwater recreational fishing, and we pose the question “Does the fact we are managing a pleasure sport mean that we need to rethink our fisheries management philosophy?” Future management of sport fish may rely less on biology and more on social science as we learn to optimize angler satisfaction. Although biology should be t...

Creel Limits in Minnesota: A Proposal for Change

Abstract Recent research has indicated that creel limits are largely ineffective in regulating recreational fish harvest in Minnesota. Current creel limits give an unrealistic picture of the biological capabilities of Minnesotas fisheries and less than 5% of angler-trips culminate with the harvesting of a creel limit. We present evidence that high creel limits may cause anglers to have unrealistic expectations of their potential harvest. When fishing success expectations are not met, the result is often dissatisfied anglers. We propose reducing creel limits to more appropriate levels by using a probability angling management strategy. These new limits would be based on past recreational harvest data from completed angler-trips. Our goal is to select creel limits that more anglers could attain, or come closer to attaining. Over time, we anticipate reduced creel limits would function more as an educational tool and may help anglers develop more realistic expectations of Minnesotas fisheries.

Field Estimation of a Lethal Oxythermal Niche Boundary for Adult Ciscoes in Minnesota Lakes

Abstract Ciscoes Coregonus artedi are coldwater stenotherms that are sensitive indicators of ecological stressors, such as eutrophication and climate warming, that reduce coldwater habitat. Temperature and oxygen profile data were collected during cisco mortality events at 17 lakes during an unusually warm summer in Minnesota in 2006. Combinations of temperature and oxygen from the profiles were mapped onto a two-dimensional niche space to directly quantify an oxythermal lethal niche boundary for ciscoes. Quantile regression was used to estimate the niche boundary that described lethal combinations of oxygen and temperature for cisco. The fitted lethal oxythermal niche boundary exhibited a curvilinear interaction between lethal temperatures and lethal oxygen concentrations. The lethal temperature under normoxia (about 8 mg/L) was estimated to be 24°C. Lethal temperatures were progressively less at lower lethal oxygen concentrations (e.g., the lethal temperature was 23.0°C at 5.0 mg/L, 22.0°C at 3.0 mg/L, ...

Landscape factors influencing lake phosphorus concentrations across Minnesota

Abstract Total phosphorus (TP) concentrations are known to be a significant factor influencing fish populations in Minnesota lakes. Consequently, a primary focus of the Minnesota Department of Natural Resources to address fish habitat in lakes across the state has been to determine relationships between TP concentrations and watershed conditions in Minnesota lakes. Because phosphorus concentrations in Minnesota lakes vary widely corresponding to differences in geomorphology, nutrient criteria were established by the Minnesota Pollution Control Agency for specific ecoregions. To refine these relationships in Minnesota lakes managed for fishing, we gathered mean summer epilimnetic TP concentrations on 1330 natural lakes to identify where agricultural and urban development have elevated phosphorus levels. Random forest, regression tree, and generalized additive models were used to model spatial variation in lake phosphorus concentrations across Minnesota. Key landscape variables known to influence TP concentrations in lakes, including lake depth and watershed size, were used as explanatory variables in these models, along with agricultural and urban development quantified for lake watersheds from the National Land Cover Dataset. These models explained up to 60% of the variation in TP in lakes across the state and showed a critical benchmark of anthropogenic land use disturbance at 40%, that once exceeded could significantly alter TP levels and consequently fish populations. This information should be useful for fish managers to prioritize conservation efforts and to set appropriate fish population goals.

Experimental Analysis of a Reduced Daily Bluegill Limit in Minnesota

Abstract The effect of a reduced daily limit (from 30 to 10 fish/d) on the size structure of bluegills Lepomis macrochirus in eight Minnesota lakes was measured with a controlled and replicated experiment. Bluegills from four treatment lakes (daily limit of 10 fish) and four control lakes (daily limit of 30 fish) were sampled in 2 years prior to regulation implementation and in the fourth and fifth years after regulation implementation. Repeated-measures analysis of variance was used to test for changes in two measures of size structure: mean length and 90th percentile length. The mean length of bluegills sampled in trap nets was significantly greater in treatment lakes than in control lakes at the end of the experiment. Bluegill 90th percentile lengths were higher during the postregulation period than the preregulation period, but not significantly so (although the P-value approached significance). Postregulation increases in length at maturity and growth rate were observed in the treatment lakes that ex...

Trophy and consumptive value-per-recruit analysis for a walleye fishery.

Abstract A utility-per-recruit model was developed to compare trophy versus food (consumptive) values of a fishery for walleyes Stizostedion vitreum in Big Sand Lake, Minnesota. Trophy value was quantified by a mail survey that asked anglers to equate a large walleye in terms of the numbers of small (2-Ib) walleyes they would have to catch to give them the same level of satisfaction. A 2-Ib walleye was assumed to have only consumptive value. Trophy values (measured in 2-Ib walleye units) of surveyed anglers increased exponentially as a function of walleye size (weight). Consumptive value was assumed to be simply the weight of the fish (divided by two to form 2-lb walleye units). Big Sand Lake anglers were classified as consumptive oriented (53.1%) or trophy oriented (46.9%). Utility- (value-) per-recruit modeling predicted that trophy value of the fishery would be maximized at lengths of entry greater than 22 in, whereas consumptive value of the fishery would be maximized at a length of entry of about 18 ...

Adapting Inland Fisheries Management to a Changing Climate

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short-term management goals with long-term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long-term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on...

Food resource effects on diel movements and body size of cisco in north‑temperate lakes

The movement patterns and body size of fishes are influenced by a host of physical and biological conditions, including temperature and oxygen, prey densities and foraging potential, growth optimization, and predation risk. Our objectives were to (1) investigate variability in vertical movement patterns of cisco (Coregonus artedi) in a variety of inland lakes using hydroacoustics, (2) explore the causal mechanisms influencing movements through the use of temperature/oxygen, foraging, growth, and predation risk models, and (3) examine factors that may contribute to variations in cisco body size by considering all available information. Our results show that cisco vertical movements vary substantially, with different populations performing normal diel vertical migrations (DVM), no DVM, and reverse DVM in lakes throughout Minnesota and northern Wisconsin, USA. Cisco populations with the smallest body size were found in lakes with lower zooplankton densities. These smaller fish showed movements to areas of highest foraging or growth potential during the day and night, despite moving out of preferred temperature and oxygen conditions and into areas of highest predation risk. In lakes with higher zooplankton densities, cisco grew larger and had movements more consistent with behavioral thermoregulation and predator avoidance, while remaining in areas with less than maximum foraging and growth potential. Furthermore, the composition of potential prey items present in each lake was also important. Cisco that performed reverse DVM consumed mostly copepods and cladocerans, while cisco that exhibited normal DVM or no migration consumed proportionally more macro-zooplankton species. Overall, our results show previously undocumented variation in migration patterns of a fish species, the mechanisms underlying those movements, and the potential impact on their growth potential.

Protecting cisco (Corego- nus artedi Leseur) oxythermal habitat from climate change: building resilience in deep lakes using a landscape approach

Cisco (Coregonus artedi Lesueur) was projected to persist in at least 171 deep, clear lakes in a climate-warmed Minnesota, U.S.A. A process-oriented, dynamic, one-dimensional yearround lake water quality model was used to predict coldwater habitat as a function of Secchi depth (a surrogate of lake productivity) and geometry ratio = As /Hmax (a measure of relative depth and strength of stratifi cation) for a series of lake types in Minnesota. Late-summer hypolimnetic oxygen concentrations were predicted to remain suffi ciently high to provide coldwater habitat within the refuge lakes even with longer durations of stratifi cation after climate warming. Catchments of refuge lakes were prioritised based on two components: 1) threat (changes in land use) and 2) investment effi ciency (total surface area of refuge lakes protected per amount invested). Priority scores were calculated for each refuge lake catchment based on the two components. Conservation strategies can be targeted in critical areas of the prioritized catchments to prevent future degradation of water quality in refuge lakes from changes in land use.

Optimal Stocking Densities of Walleye Fingerlings in Minnesota Lakes

Abstract A generalized additive model was developed that described the effects of fingerling stocking density on the abundance of walleyes Sander vitreus in 551 lakes in Minnesota. Walleye abundance was measured as a catch per effort (CPE) from 1,511 standard Minnesota Department of Natural Resources gill-net assessments conducted during 1986–2004. In addition to fingerling stocking, the effects of lake morphometry, productivity, and fish community variables on walleye CPE were also described using a generalized additive model. Lake morphometry variables had sharply nonlinear effects on walleye abundance. Walleye abundance declined in lakes with areas less than 1,000 acres and increased rapidly in lakes with depths of less than 30 ft. The lake productivity variable, total alkalinity, was positively related to walleye abundance. Abundance of northern pike Esox lucius had a negative effect and abundance of yellow perch Perca flavescens a positive effect on walleye abundance. The response of walleye abundanc...