No abstract

No abstract

The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture–recapture‐based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid‐1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age‐2 and older fish are age dependent but apparently not time dependent. Back‐calculation of recruitment using the apparent 1990s population age structure implies periods of higher recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and Wildlife Service recovery criterion of stable abundance is not being met for this population. Also, there is a critical need to develop new abundance indexing and tagging methods so that early, reliable, and rapid estimates of humpback chub recruitment can be obtained to evaluate population responses to management actions designed to facilitate the restoration of Colorado River native fish communities.

RESUMEN: Las poblaciones de la lamprea del Pacífico (Entosphenus tridentatus) están declinando en la cuenca del Río Columbia, y desde el año 2000 se ha implementado la translocación de individuos adultos para restablecer los corredores migratorios de esta especie. Se describen y reportan los resultados de dos programas recientes de translocación, se contextualiza el uso de la translocación y se discuten sus beneficios potenciales, riesgos e incertidumbre. Ambos programas de translocación parecen haber incrementado el número de adultos desovantes y la presencia tanto de larvas como de juveniles; sin embargo, para que sea posible cualquier incremento ulterior en el stock natural de reproductores se requerirá de al menos una, aunque muy probablemente de más, generaciones. Se observó que el número de adultos que ingresó al Río Umatilla aumentó en los primeros cuatro años después de la primera translocación. Los beneficios potenciales de los programas de translocación son un aumento en la producción de feromonas por parte de larvas ammocoetes para atraer adultos, incremento en la distribución y abundancia de lampreas en áreas objetivas, incremento en la cantidad de nutrientes derivados del medio marino y la promoción de culturas tribales. Los riesgos potenciales incluyen modificación de la estructura poblacional y las adaptaciones genéticas asociadas, transmisión de enfermedades y agotamiento de los stocks donadores. ABSTRACT: The Pacific lamprey (Entosphenus tridentatus) is in decline in the Columbia River Basin, and translocating adult lamprey to bypass difficult migration corridors has beenimplemented since 2000. We describe and report results from two current translocation programs, provide context for use of translocation, and discuss potential benefits, risks, and uncertainties. Both translocation programs appear to have increased the number of spawning adults and the presence of larvae and juveniles; however, any subsequent increase in naturally spawning adults will require at least one, and likely more, generations to be realized. It was seen that the number of adults entering the Umatilla River increased beginning four years after the first translocations. Potential benefits of translocation programs are increased pheromone production by ammocoetes to attract adults, increased lamprey distribution and abundance in target areas, increased marine-derived nutrients, and promotion of tribal culture. Potential risks include disruption of population structure and associated genetic adaptations, disease transmission, and depletion of donor stocks.

Predation by large northern pikeminnow (formerly northern squawfish) Ptychocheilus oregonensis is a major source of mortality for juvenile salmonids Oncorhynchus spp. in the lower Columbia and Snake rivers. Large‐scale, agency‐operated fisheries have been implemented in this area since 1990 to harvest northern pikeminnow with a goal of 10–20% exploitation. We used indirect methods to analyze the success of the fisheries, and examined benefits to salmonid populations. From 1991 to 1996, three fisheries (sport‐reward, dam‐angling, and gill‐net) harvested approximately 1.1 million northern pikeminnow that were 250 mm in fork length or longer, with the sport‐reward fishery contributing 86.5% of the total catch. Total exploitation averaged 12.0% (range, 8.1–15.5) for 1991–1996 and met program goals in all years except 1993. Gill‐net and dam‐angling fisheries harvested larger northern pikeminnow (which consume a greater number of juvenile salmonids) than the sport‐reward fishery. Modeling results indicate that potential predation on juvenile salmonids by northern pikeminnow has decreased 25% since fishery implementation. The relative benefits of a given exploitation rate decreased with time as the number of large northern pikeminnow was reduced; however, additional reductions in potential predation are probable if exploitation is maintained at mean 1994–1996 levels. We estimate a reduction in potential predation of 3.8 million juvenile salmonids (representing 1.9% of the total population) if exploitation rates are maintained at mean 1991–1996 levels. Continued monitoring of predator populations is prudent, and we recommend that restoration and enhancement of Columbia River basin salmonids not rely solely on any one management approach.

No abstract

Using critical thermal maximum (CTMax) tests, we examined the relationship between upper temperature tolerances and fish size (fry–adult or subadult lengths) of rainbow trout Oncorhynchus mykiss (41–200‐mm TL), Apache trout O. gilae apache (40–220‐mm TL), largemouth bass Micropterus salmoides (72–266‐mm TL), Nile tilapia Oreochromis niloticus (35–206‐mm TL), channel catfish Ictalurus punctatus (62–264 mm‐TL), and Rio Grande cutthroat trout O. clarkii virginalis (36–181‐mm TL). Rainbow trout and Apache trout were acclimated at 18°C, Rio Grande cutthroat trout were acclimated at 14°C, and Nile tilapia, largemouth bass, and channel catfish were acclimated at 25°C, all for 14 d. Critical thermal maximum temperatures were estimated and data were analyzed using simple linear regression. There was no significant relationship (P > 0.05) between thermal tolerance and length for Nile tilapia (P = 0.33), channel catfish (P = 0.55), rainbow trout (P = 0.76), or largemouth bass (P = 0.93) for the length ranges we tested. There was a significant negative relationship between thermal tolerance and length for Rio Grande cutthroat trout (R2 = 0.412, P < 0.001) and Apache trout (R2 = 0.1374, P = 0.028); however, the difference was less than 1°C across all lengths of Apache trout tested and about 1.3°C across all lengths of Rio Grande cutthroat trout tested. Because there was either no or at most a slight relationship between upper thermal tolerance and size, management and research decisions based on upper thermal tolerance should be similar for the range of sizes within each species we tested. However, the different sizes we tested only encompassed life stages ranging from fry to adult/subadult, so thermal tolerance of eggs, alevins, and larger adults should also be considered before making management decisions affecting an entire species.

We quantified tag retention, survival, and growth in juvenile, captive‐reared Humpback Chub Gila cypha marked with three different tag types: (1) Biomark 12.5‐mm, 134.2‐kHz, full duplex PIT tags injected into the body cavity with a 12‐gauge needle; (2) Biomark 8.4‐mm, 134.2‐kHz, full duplex PIT tags injected with a 16‐gauge needle; and (3) Northwest Marine Technology visible implant elastomer (VIE) tags injected under the skin with a 29‐gauge needle. Estimates of tag loss, tagging‐induced mortality, and growth were evaluated for 60 d with each tag type for four different size‐groups of fish: 40–49 mm, 50–59 mm, 60–69 mm, and 70–79 mm TL. Total length was a significant predictor of the probability of PIT tag retention and mortality for both 8‐mm and 12‐mm PIT tags, and the smallest fish had the highest rates of tag loss (12.5–30.0%) and mortality (7.5–20.0%). Humpback Chub of sizes 40–49 mm TL and tagged with VIE tags had no mortality but did have a 17.5% tag loss. Growth rates of all tagged fish were similar to controls. Our data indicate Humpback Chub can be effectively tagged using either 8‐mm or 12‐mm PIT tags with little tag loss or mortality at sizes as low as 65 mm TL. Received July 24, 2014; accepted October 31, 2014