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<br />Table 8. Fecundity of razorback suckers collected in 1964 from the Green Riuer in Dinosaur National Monument
<br />
<br />Location of
<br />captures Date of
<br />capture
<br />(1964)
<br />Total
<br />length (mm)
<br />Weight
<br />(g)
<br />Estimated total
<br />no. of eggs
<br />Island Park (4) 21 Aug. 534 1,524 72,476
<br />Downstream from 4 5 Sept. 530 1;437 41,119
<br />Island Park (4) 1 Nov. 529 1,317 25,5436
<br />Unknown - 519 1,560 69,460
<br />Unknown - 516 1,380 37,665
<br />Downstream from 4 5 Sept. 513 1,570 30,854
<br />Island Park (4) 1 Nov. 505 1,145 42,522
<br />Unknown - 485 1,360 76,576
<br />Echo Park (3) 31 Oct. 470 990 27,614
<br />Unknown - 466 1,100 44,084
<br />Average 507 1,338 46
<br />740
<br />SD 24.8 201.4 ,
<br />19, 201
<br />aSee Fig. 1 for locations of stations.
<br />6Tota1 count (actual) of maturing eggs was 24,490.
<br />Total count (actual) of maturing eggs was 44,624.
<br />error was only 3 to 4%-not enough to account for the
<br />wide variability in fecundity. We attempted to relate
<br />fecundity to total length and fecundity with a loga-
<br />rithmic equation (Bagena11967). However, the relation
<br />was not significant; rather, it appeared to be random.
<br />The estimated numbers of eggs per female ranged
<br />from 27,614 to 76,576 (Table 8-.
<br />Spawning Period
<br />Before the construction of large dams, razorback
<br />suckers made extensive spawning migrations in early
<br />spring. Jordan (1891) reported that razorback suckers
<br />ascended the Rio Animas in the spring of 1891 for
<br />spawning, and Chamberlain (1904) cited reports by
<br />early settlers in Arizona that the suckers congregated
<br />in tributary streams. After the damming of the rivers
<br />in the lower basin, these migrations were blocked, but
<br />apparently the suckers then spawned in reservoirs.
<br />Douglas (1952) observed spawning in Lake Havasu
<br />in March 1950. Razorback suckers moved into shallow
<br />coves of the lake, where water depths ranged from 25
<br />to 50 cm and surface water temperatures from 14 to
<br />18 C. Individual females accompanied by two to six
<br />males swam over the bottom of the cove in small
<br />circles. Males remained close to responsive females as
<br />they swam about. The fish occasionally settled to the
<br />bottom, vibrating their bodies rapidly. Gametes were
<br />presumably emitted at this time, but the fish were no
<br />longer visible because silt disturbed by the spawning
<br />fish roiled the water.
<br />Jonez and Sumner (1954), who observed spawning
<br />razorback suckers in Lake Mead between 1 March and
<br />15 April 1953, described an extensive shoreward
<br />movement during the spawning season, especially in
<br />the vicinity of river mouths. Water temperatures
<br />ranged from 12 to 18 C during this period. Spawning
<br />appeared widespread along gravel shores at depths of
<br />0.6 to 5 m. Actions of spawning fish were similar to
<br />those described by Douglas (1952-.
<br />Jonez and Sumner (1954) reported what they iden-
<br />tified as small razorback suckers below Davis Dam in
<br />1950 and believed that predation on the freshly
<br />spawned eggs limited reproductive success in Lake
<br />Mojave.
<br />More recently, spawning by razorback suckers was
<br />reported in these same reservoirs, but the young were
<br />not found, suggesting that reproductive success was
<br />poor (Minckley 1973-. However, some successful repro-
<br />duction must have occurred after the reservoirs were
<br />impounded, because adults are still found.
<br />Poor reproductive success has also been reported in
<br />the upper basin (Banks 1964; Vanicek et al. 1970;
<br />Holden and Stalnaker 1975a, 1975b-. The apparent
<br />lack of young of the year and juveniles in collections
<br />can perhaps be attributed, at least in part, to their
<br />close resemblance to young flannelmouth suckers. The
<br />few young-of-the-year and age I razorback suckers
<br />that might have been collected could easily have been
<br />overlooked among the large numbers of juvenile
<br />flannelmouth suckers that we caught. Conversely, sub-
<br />adult razorback suckers should have been easily recog-
<br />nized by the bony nape if they had been collected. P. B.
<br />Holden (unpublished data) collected a few subadult
<br />fish, but none were collected during 1974-76. In the
<br />summer of 1977, Holden (1978) collected two juvenile
<br />catostomids that were tentatively identified as razor-
<br />back suckers.
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