Evidence for Shifts in Growth and Development of Channel Catfish in Response to Removal Efforts in the San Juan River, New Mexico

The introduction of non-native fishes into the San Juan River, NM has been attributed to the decline of many native fish populations.  In particular the razorback sucker and Colorado pikeminnow have been listed as endangered since 1991.  “Non-native fish species can impact native fish species through indirect competitive resource interactions or direct predation.  In the San Juan River system species such as Common carp, bullhead and channel catfish were introduced in 1880 and were commonly seen by 1910.  The success of these introduced species is associated with the decline of native species and by 1960 the razorback suckers and Colorado pikeminnow were rarely seen in the lower portion on the river basin.  Although many non-native species are now common in the San Juan River, channel catfish are of the greatest concern due to their widespread distribution, high abundance and presumed predation on native fishes.  Monitoring studies of adult fish in the San Juan River demonstrated that channel catfish accounted for the largest percentage of large bodied fish in the system (i.e. 47.6% of total catch).  Due to the exploitation of native species by channel catfish, management actions were established to mitigate the effects of non-native fishes, and quantify impacts of non-native fish piscivory.  Although removal efforts have been successful in reducing the number of large channel catfish (>300mm) populations of stocked endangered fishes still struggle with successful recruitment.  This may be tied invasive species interactions or the effects of the removal practices currently in place.  Data suggest that the techniques used in non-native fish removal can exclude younger age classes and potentially cause an overall shift in the size and age of the invasive species population.  The process of non-native fish removal that is size selective is indicative of another strategy used to determine maximum sustained yield (MSY) for marine and freshwater fisheries.  Overharvest of a fishery can result in (1) declines in yield (2) increases in the proportion of small fish in the commercial harvest, (3) a narrow range of age groups represented in the fishery.  

The objectives of this research are to: 

1. Determine the age structure with relation to body length and weight for channel catfish in the San Juan River.
2. Determine how age and size are associated with stage of maturation
3. Determine if a shift in size at age or size at maturation has occured in the San Juan River, NM since 2001.