Patrick J. Martinez

Fish species composition before and after construction of a main stem reservoir on the White River, Colorado

SynopsisThe completion in the fall of 1984 of Taylor Draw Dam on the White River, Colorado, formed Kenney Reservoir — thus impounding the last significant free-flowing tributary in the Upper Colorado River Basin. Fishes were sampled above and below the dam axis prior to closure of the dam and in the reservoir and river downstream following impoundment. While immediate effects of the dam to the ichthyofauna included blockage of upstream migration to 80 km of documented range for endangered Colorado squawfish, the reservoir also proved to have profound delayed effects on the rivers species composition. Pre-impoundment investigations in 1983–1984 showed strong domination by native species above, within, and below the reservoir basin. By 1989–1990, non-native species comprised roughly 90% of the fishes collected in the reservoir and 80% of the fishes collected in the river below the dam. Initially, fathead minnow, whose numbers quickly increased in the new reservoir, dominated all post-impoundment collections, but red shiner became the most abundant fish collected in the river below the dam by 1989–1990. While agency stocking programs for the reservoir sought to emphasize a sport fishery for salmonids, primarily rainbow trout, local enthusiasm for warmwater sport fishes resulted in illicit transfers of these species from nearby impoundments. Several species, formerly rare or unreported in the White River in Colorado, including white sucker, northern pike, green sunfish, bluegill, largemouth bass and black crappie, were present in the river following impoundment. Our investigation indicates smaller-scale, main-stem impoundments that do not radically alter hydrologic or thermal regimes can still have a profound influence on native ichthyofauna by facilitating establishment and proliferation of nonnative species.

Western Lake Trout Woes

Abstract In the western United States, the ability of non-native lake trout (Salvelinus namaycush) to attain large sizes, > 18 kg under favorable conditions, fueled the popularity of lake trout fisheries. In the past, restrictive regulations were adopted to increase lake trout abundance and produce trophy specimens. More recently, lake trout have become increasingly problematic because they prey upon and potentially compete with native and sport fishes. We review the experiences of agencies in seven western states which are considering or implementing strategies to address lake trout impacts despite management difficulties due to mixed public perception about lake trouts complex interactions with native or introduced fauna. Special regulations protecting lake trout have often been liberalized or rescinded to encourage their harvest and reduce their negative effects. More intensive methods to control or reduce lake trout abundance include promoting or requiring lake trout harvest, commercial-scale netting...

Are we doing all we can to Stem the Tide of Illegal Fish Stocking

They’ve been called “bucket biologists” or “midnight managers” but these nicknames belie the ignorance and selfishness of individuals who engage in illegal stocking. Their actions are defeating multi-million dollar native fish recovery projects, damaging sustainable recreational fisheries worth billions of dollars, threatening native species with extinction, and diverting dwindling agency resources away from programs that benefit fishing and aquatic resources into expensive and often perpetual remediation programs. Illegal stocking is creating a growing burden on agencies and on society, and its impacts can be irreversible. The problem is global and yet there appears to be little collaboration across jurisdictions to seek solutions. We contend that the fisheries profession can and must do a better job of preventing illegal fish stocking through more strategic education programs, proactive regulatory policy, universally severe penalties, an international reward pool, and inter-jurisdictional collaboration. hoW Big iS thiS pRoBleM?

Elemental signatures in otoliths of hatchery rainbow trout (Oncorhynchus mykiss): distinctiveness and utility for detecting origins and movement

Otolith chemistry in freshwater has considerable potential to reveal patterns of origin and movement, which would benefit traditional fisheries management and provide a valuable tool to curb the sp...

Selecting Harvest Regulations for Recreational Fisheries: Opportunities for Research/Management Cooperation

Abstract The need for harvest regulations to manage sportfisheries is widely recognized, but regulations are not always selected and applied scientifically with an assessment of the ecological implications of manipulating harvest. Regulations directed at protecting top predator fishes may have undesirable consequences for other fishes in the system. A strategy is developed for selecting harvest regulations that considers both direct effects of regulations on the target population and indirect effects on other trophic levels. The result is a set of regulation options that achieve angler and management goals while reducing unexpected or adverse responses within the fish community. This approach requires fishery researchers and managers to work closely together to be effective, and, thus, the regulation selection process offers an excellent opportunity for research and management cooperation.

Sources of Nonnative Centrarchids in the Upper Colorado River Revealed by Stable Isotope and Microchemical Analyses of Otoliths

Abstract Nonnative fishes represent a significant impediment to the recovery of imperiled fishes, including those endemic to the Colorado River in the southwestern United States. Efforts to control nonindigenous fish abundance in the upper Colorado River basin have been unsuccessful owing in part to lack of knowledge regarding nonnative fish recruitment sources. We determined the source habitat (floodplain pond versus riverine habitats) for nonnative centrarchid fishes (largemouth bass Micropterus salmoides, green sunfish Lepomis cyanellus, bluegill L. macrochirus, and black crappie Pomoxis nigromaculatus) in the upper Colorado River using stable hydrogen isotopic composition (δD) and strontium: Calcium (Sr: Ca) ratios in fish otoliths as natural markers of environmental history. Stable hydrogen isotope analysis revealed that 59% of centrarchids exhibited the otolith core signatures expected for riverine-origin fish, while 22% had emigrated from floodplain ponds and 19% were of uncertain origin. Strontium...

Tracking Trophic Interactions in Coldwater Reservoirs Using Naturally Occurring Stable Isotopes

Abstract We measured signatures of naturally occurring stable isotopes of carbon (13C) and nitrogen (15N) in important invertebrate and fish taxa in two coldwater reservoirs in Colorado that had different food webs. One reservoir, Lake Granby, contained a large population of an opossum shrimp, Mysis relicta, and the other, Blue Mesa Reservoir, did not. We compared temporal dynamics of isotopic signatures of all taxa between lakes to quantify sources of variability in consumer signatures and to assess potential turnover rates of isotopic signatures in the top predator. Stable isotope signatures varied little across season or body size within most taxa, but large differences across reservoirs were observed. Nitrogen signatures of lake trout Salvelinus namaycush were enriched in larger individuals in both reservoirs, indicating increasing trophic position with body size. Carbon signatures in lake trout livers were consistently lower than those in muscle samples but did not change more rapidly than muscle sig...

Some Factors Affecting a Hatchery-Sustained Kokanee Population in a Fluctuating Colorado Reservoir

Abstract The population of kokanees Oncorhynchus nerka in Lake Granby, Colorado, is expected to satisfy the competing demands of providing summer harvest for anglers, kokanee eggs for restocking. and prey for trophy lake trout Salvelinus namaycush In the late 1970s. declines in numbers of kokanees harvested and kokanee eggs collected prompted investigations of the influences of stocking rates, reservoir fluctuations, competition with Mysis relicta, and lake trout predation. The kokanee population has been maintained mainly by annual stocking of fry (≤30 mm total length. TL) since 1951. When maturing spawners exceeded 367 mm TL, more than 50% of them were harvested in the summer recreational fishery. which reduced the number of kokanees in some fall spawning runs. However. when maturing year-classes were composed mainly of smaller kokanees. proportionately fewer were harvested. and the number of maturing kokanees entering the spawning run increased. Despite a trend of increased stocking from 1951 to 1978. ...

Native fish conservation areas: A vision for large-scale conservation of native fish communities

Abstract The status of freshwater fishes continues to decline despite substantial conservation efforts to reverse this trend and recover threatened and endangered aquatic species. Lack of success is partially due to working at smaller spatial scales and focusing on habitats and species that are already degraded. Protecting entire watersheds and aquatic communities, which we term “native fish conservation areas” (NFCAs), would complement existing conservation efforts by protecting intact aquatic communities while allowing compatible uses. Four critical elements need to be met within a NFCA: (1) maintain processes that create habitat complexity, diversity, and connectivity; (2) nurture all of the life history stages of the fishes being protected; (3) include a long-term enough watershed to provide long-term persistence of native fish populations; and (4) provide management that is sustainable over time. We describe how a network of protected watersheds could be created that would anchor aquatic conservation...

Proposed Biological Management of Mysis relicta in Colorado Lakes and Reservoirs

Abstract The opossum shrimp Mysis relicta has been introduced into many lakes and reservoirs outside its native range to supplement the prey bases for fish. Colorado has received more introductions of the mysid than any other state or province in western North America, but not all of these introductions have been beneficial or innocuous. Mysid predation on zooplankton, particularly cladocerans, has resulted in diminished food for some fishes, especially for planktivores such as the kokanee Oncorhynchus nerka and small trout Oncorhynchus spp. Few fishes forage on the often abundant populations of introduced mysids. Management options are limited in lakes where M. relicta competes for, or has eliminated, the large zooplankters eaten by fish. Furthermore, the mysid has shown enough vagility to expand its nonnative range and may harm fisheries in waters that it enters. Because its eradication is not now feasible, the development of strategies to control or benefit from established mysid populations is warrant...