Aravaipa Creek is a special place as it has the richest intact native fish fauna remaining within the Lower Colorado basin with seven native species. Relative to historical conditions this is not a very high richness value. Sites such as the Salt River at Tempe and in the Salt River Canyon had 14 and 12 natives respectively, while the upper San Pedro River had between 11-12 species. Today, none persist at Tempe, few occur in the Salt River Canyon and the upper San Pedro has only 3-4 species, with one being very restricted in occurrence.
Species diversity changes depending upon where you are sampling. In the upper end you may seine all 7 natives in one haul. Within the middle section speckled dace are fairly uncommon, and spikedace are not usually found at all three sites. In the lower end longfin dace tends to dominate, the loach minnow, two suckers and roundtail chub are sometimes abundant. Spikedace are very rare and speckled dace have not been recorded from this reach in many years.
The majority of individuals of the introduced species are usually recorded from the lower 5 sites, but the three more common species can at times be found anywhere within the system. Fathead minnow are typically only rarely found at the lowermost site, while mosquitofish can be abundant at times, but again usually only at the lowermost site. Yellow bullhead are relatively difficult to seine, but are probably quite abundant in certain reaches. Green sunfish within Aravaipa Creek also tend to live in difficult to seine places, but are more easily caught. Both species tend to be found in deeper undercut banks with little obvious water movement and slower side eddies with thick cover (typically tree roots). Specific sampling of that habitat will often reveal a surprising abundance of both species. Red shiner can be very patchy, and some years they are quite rare, at other times they can be quite common at the lower most site..
Each species tends to be found within distinctive habitats within the creek, although on occasion we have seined all seven natives in one haul. Typically, Tiaroga inhabit the fastest sections of the creek within riffles. Rhinichthys and Pantosteus also tend to inhabit relative fast flowing water, with the latter preferring deeper fast sections. Meda and Agosia are generally found in the tails of riffles, or in runs. Both Gila and Catostomus tend to predominately inhabit pools. Both yellow bullhead and green sunfish tend to be found in the lower reaches of the creek in deeper undercut banks often with little obvious water movement and slower side eddies with thick cover (typically tree roots). Specific sampling of that habitat will often reveal a surprising abundance of both species. Each habitat type typically requires a different seining technique. Within faster riffles we usually kick seine. This is done with two people holding the seine in place across the creek, being sure the lead line is on the bottom, then 2-5 people shuffle their feet and work their way downstream to the edge of the net at which point everyone lifts the net. For riffles, runs, and pools two people usually toss the seine upstream, then pull it downstream, moving slightly quicker than the water. After a short distance it can be lifted, or one person swings onto the bank. For some pools it is profitable to have a second seine set downstream to prevent fishes from moving downstream. The first seine is pulled downstream into the second seine and lifted together. The key thing to remember when sampling is always be prepared to adapt to the situation, and feel free to try something different as you'll be surprised by what you might catch.
Photos from previous trips to Aravaipa Creek can be found here. In addition to links to pictures provided immediately below (the |P| links), some useful links to pictures can also be found in the identification section below, and the sampling strategy section above.
The suckers are easily recognized by their peculiar sub-terminal mouths, larger scales and often large size. The two species are easily differentiated. Pantosteus (pans or desert sucker) are distinguished from Catostomus (cats or Sonoran sucker) by having smaller scales, a much broader blunter head (when viewed from above), and most obviously a cartilaginous plate inside their jaws.
Agosia (longfin dace) is often the most common minnow, it has a darkish mid lateral band, a somewhat distinctive spot on the caudal peduncle and has a moderately chuby body. They are most easily confused with Meda (spikedace) or small Gila (roundtail chub). Small Gila can be identified by having a more deeply forked caudal fin than any other Aravaipa native species, and their bodies are quite silvery. Larger specimens are obvious since they are the only minnow that grows over about 80 mm in Aravaipa. Meda are a slender bodied species, with very silvery coloration and fine black specks. At the front and rear of the dorsal fin there is a broad distinctive spot that can easily be seen when viewed from above. Around spawning season they have a strong brassy or golden hue along their sides. Meda are also the only minnow which has a spine in its dorsal fin. It is best to learn the other characteristics for this species though rather than always checking for a spine as you are more likely to damage the fish. Tiaroga (loach minnow) and Rhinichthys (rhinos or speckled dace) look very similar, both have mottled coloration, are ventrally flattened for life on the substrate, and both tend to get a lot of red on their fins during spawning season, although this is much stronger in loach minnow. Tiaroga has two pairs of spots, one pair with one spot each behind and in front of the dorsal fin (similar to Meda), the other pair is on the margins of the caudal peduncle at the caudal fin base. Rhinichthys lacks these spots.
Most of the introduced species are easily identified. Yellow bullhead have a spine in their dorsal and pectoral fins, obvious barbels and an adipose fin. Green sunfish are a deep bodied fish with numerous spines in their dorsal and anal fins. Red shiner have much larger scales than the native minnows, tend to be deeper bodied, and during the warmer months males have bright red fins and a purplish hue to their body. Fathead minnows are quite rare and somewhat difficult for an untrained eye to distinguish from Agosia. Fatheads also look very different between the sexes, and also between sizes. Gambusia tend to live in the shallows along the streams margins at the waters surface. They have an upturned mouth for surface feeding. Females are often quite fat as they carry their young which are born alive. Males are quite small and have modified their anal fin into a gonopodium for internally fertilizing females.