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~ (q<[q \[ CA.\~ 1J ~1L1'Z INFORMAL LARVAI.JYOY HUMPBACK CHUB SURVEY Field Notes and Observations Richard Valdez May 21-22, 1989 INTRODUcnON At the request of B. Persons (AGF) I conducted an informal survey of the lower reaches of the Little Colorado River in search of larva1 and YOY humpback chub on Sunday, May 21 and Monday, May 22, 1989. I made several collections of fish with a small aquarium net attached to the opposite end of a batchery dip neL Most of the fish were captured where they were sighted along shallow shorelines and with blind sweeps in small pocketwaters. At each collection site, J recorded location, habitat description, associated cover, and species composition, along with a photograph of the habitaL I estimated water depth and velocity. Larval and YOY fish were tentatively identified with the aid of a hand-held lens; most could only be sorted to fami1y Catstomidae or Cyprinidae, although speckled dace (Rhinichthys osculus) were distinct enough to identify, and the humpback chub (Gila ~ were sufficiently large to distinguish from other cyprinids. Further eDImination also revealed the presence of bluehead suckers (pantosteus discobolus). This is a qualitative analysis and my estimates of depth and velocity. as well as my assessment of substrate and habitat type are intended only to provide a perspective on the habitat types used by the various sympatric species of the LCR. In my opinion, it is feasible to perform habitat-use analyses on the young cbubs in the LCR and compare with available habitats in other tributaries as well as in the main Colorado River. OBSERVATIONS The habitats in which I found post-Iarval humpback chub (-15-30 mm n.) were distinct from those habitats in which I captured Iarval and post-larval speckled dace and suckers. The YOY humpback chub were usually along shoreline boulder pocketwaters in much deeper water than the other fish species (see Plate 6). The speckled dace were usually in shallow cobble areas (plate 1), while the suckers were in shallow sand/silt shorelines (plate 2) or in shallow boulder pocketwaters. No humpback chub were found in the shaUow backwaters of the LCR (only three backwaters were found in this survey). Species found in tbe backwater habitats of the LCR were post-1arva1 and one-year old bluehead suckers; and post-larval, juvenile and adult speckled dace. The only exception to this was the discovery of 500 to 750 YOY humpback chub in a flow-thrOUgh backwater located at the outlet of the Little Colorado River (plate 8). Their presence in this backwater may be explained by the relatively higher water temperatures in this habitaL It appears that these fish were transPOrted from the LCR and had staged in this area in response to the flow fluctuations of the main Colorado River. This specific area at the mouth of the LCR may be important to tbe young humpback chub following their Iarval stage of developmenL A s11D1Dlaly of my observations shows that the post-larval humpback chub in the LCR were in water that ranged from 6 to 48 inches in depth, 0 to 1 ips velocity, and were found primarily over boulder/silt substrates (Table 1). In contrast, the post-Iarval speckled dace were in 2 to 10 inches of water. 0 to 0.3 ips velocity, and over sand/silt substrate. The Iarval and post-Iarval suckers were in very shallow, open water shoreline habitats ranging in depth from 0.5 to 10 inches, with 0 to 0.3 ips velocity, and over sand/silt substrate, often associated with vegetation. 1 ~